Remove TTML package from null-checking blacklist

PiperOrigin-RevId: 290629644

Remove TTML package from null-checking blacklist
PiperOrigin-RevId: 290629644
37908dd4 · ibaker · Ian Baker · 8a2a5271 · 37908dd4 · 37908dd4
Commit 37908dd4 authored Jan 20, 2020 by ibaker Committed by Ian Baker Jan 24, 2020
Showing with 107 additions and 68 deletions
library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlDecoder.java
library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlNode.java
library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlRenderUtil.java
library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlStyle.java
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlDecoder.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlDecoder.java
@@ -16,11 +16,13 @@
 package com.google.android.exoplayer2.text.ttml;
 import android.text.Layout;
+import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.text.Cue;
 import com.google.android.exoplayer2.text.SimpleSubtitleDecoder;
 import com.google.android.exoplayer2.text.Subtitle;
 import com.google.android.exoplayer2.text.SubtitleDecoderException;
+import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.ColorParser;
 import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.Util;
@@ -32,6 +34,7 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import org.checkerframework.checker.nullness.qual.PolyNull;
 import org.xmlpull.v1.XmlPullParser;
 import org.xmlpull.v1.XmlPullParserException;
 import org.xmlpull.v1.XmlPullParserFactory;
@@ -110,18 +113,18 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
      Map<String, TtmlStyle> globalStyles = new HashMap<>();
      Map<String, TtmlRegion> regionMap = new HashMap<>();
      Map<String, String> imageMap = new HashMap<>();
-      regionMap.put(TtmlNode.ANONYMOUS_REGION_ID, new TtmlRegion(null));
+      regionMap.put(TtmlNode.ANONYMOUS_REGION_ID, new TtmlRegion(TtmlNode.ANONYMOUS_REGION_ID));
      ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes, 0, length);
      xmlParser.setInput(inputStream, null);
-      TtmlSubtitle ttmlSubtitle = null;
+      @Nullable TtmlSubtitle ttmlSubtitle = null;
      ArrayDeque<TtmlNode> nodeStack = new ArrayDeque<>();
      int unsupportedNodeDepth = 0;
      int eventType = xmlParser.getEventType();
      FrameAndTickRate frameAndTickRate = DEFAULT_FRAME_AND_TICK_RATE;
      CellResolution cellResolution = DEFAULT_CELL_RESOLUTION;
-      TtsExtent ttsExtent = null;
+      @Nullable TtsExtent ttsExtent = null;
      while (eventType != XmlPullParser.END_DOCUMENT) {
-        TtmlNode parent = nodeStack.peek();
+        @Nullable TtmlNode parent = nodeStack.peek();
        if (unsupportedNodeDepth == 0) {
          String name = xmlParser.getName();
          if (eventType == XmlPullParser.START_TAG) {
@@ -149,10 +152,12 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
              }
            }
          } else if (eventType == XmlPullParser.TEXT) {
-            parent.addChild(TtmlNode.buildTextNode(xmlParser.getText()));
+            Assertions.checkNotNull(parent).addChild(TtmlNode.buildTextNode(xmlParser.getText()));
          } else if (eventType == XmlPullParser.END_TAG) {
            if (xmlParser.getName().equals(TtmlNode.TAG_TT)) {
-              ttmlSubtitle = new TtmlSubtitle(nodeStack.peek(), globalStyles, regionMap, imageMap);
+              ttmlSubtitle =
+                  new TtmlSubtitle(
+                      Assertions.checkNotNull(nodeStack.peek()), globalStyles, regionMap, imageMap);
            }
            nodeStack.pop();
          }
@@ -166,7 +171,11 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
        xmlParser.next();
        eventType = xmlParser.getEventType();
      }
+      if (ttmlSubtitle != null) {
        return ttmlSubtitle;
+      } else {
+        throw new SubtitleDecoderException("No TTML subtitles found");
+      }
    } catch (XmlPullParserException xppe) {
      throw new SubtitleDecoderException("Unable to decode source", xppe);
    } catch (IOException e) {
@@ -221,8 +230,8 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
      return defaultValue;
    }
    try {
-      int columns = Integer.parseInt(cellResolutionMatcher.group(1));
+      int columns = Integer.parseInt(Assertions.checkNotNull(cellResolutionMatcher.group(1)));
-      int rows = Integer.parseInt(cellResolutionMatcher.group(2));
+      int rows = Integer.parseInt(Assertions.checkNotNull(cellResolutionMatcher.group(2)));
      if (columns == 0 || rows == 0) {
        throw new SubtitleDecoderException("Invalid cell resolution " + columns + " " + rows);
      }
@@ -233,7 +242,9 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    }
  }
+  @Nullable
  private TtsExtent parseTtsExtent(XmlPullParser xmlParser) {
+    @Nullable
    String ttsExtent = XmlPullParserUtil.getAttributeValue(xmlParser, TtmlNode.ATTR_TTS_EXTENT);
    if (ttsExtent == null) {
      return null;
@@ -245,8 +256,8 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
      return null;
    }
    try {
-      int width = Integer.parseInt(extentMatcher.group(1));
+      int width = Integer.parseInt(Assertions.checkNotNull(extentMatcher.group(1)));
-      int height = Integer.parseInt(extentMatcher.group(2));
+      int height = Integer.parseInt(Assertions.checkNotNull(extentMatcher.group(2)));
      return new TtsExtent(width, height);
    } catch (NumberFormatException e) {
      Log.w(TAG, "Ignoring malformed tts extent: " + ttsExtent);
@@ -258,24 +269,26 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
      XmlPullParser xmlParser,
      Map<String, TtmlStyle> globalStyles,
      CellResolution cellResolution,
-      TtsExtent ttsExtent,
+      @Nullable TtsExtent ttsExtent,
      Map<String, TtmlRegion> globalRegions,
      Map<String, String> imageMap)
      throws IOException, XmlPullParserException {
    do {
      xmlParser.next();
      if (XmlPullParserUtil.isStartTag(xmlParser, TtmlNode.TAG_STYLE)) {
-        String parentStyleId = XmlPullParserUtil.getAttributeValue(xmlParser, ATTR_STYLE);
+        @Nullable String parentStyleId = XmlPullParserUtil.getAttributeValue(xmlParser, ATTR_STYLE);
        TtmlStyle style = parseStyleAttributes(xmlParser, new TtmlStyle());
        if (parentStyleId != null) {
          for (String id : parseStyleIds(parentStyleId)) {
            style.chain(globalStyles.get(id));
          }
        }
-        if (style.getId() != null) {
+        String styleId = style.getId();
-          globalStyles.put(style.getId(), style);
+        if (styleId != null) {
+          globalStyles.put(styleId, style);
        }
      } else if (XmlPullParserUtil.isStartTag(xmlParser, TtmlNode.TAG_REGION)) {
+        @Nullable
        TtmlRegion ttmlRegion = parseRegionAttributes(xmlParser, cellResolution, ttsExtent);
        if (ttmlRegion != null) {
          globalRegions.put(ttmlRegion.id, ttmlRegion);
@@ -292,7 +305,7 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    do {
      xmlParser.next();
      if (XmlPullParserUtil.isStartTag(xmlParser, TtmlNode.TAG_IMAGE)) {
-        String id = XmlPullParserUtil.getAttributeValue(xmlParser, "id");
+        @Nullable String id = XmlPullParserUtil.getAttributeValue(xmlParser, "id");
        if (id != null) {
          String encodedBitmapData = xmlParser.nextText();
          imageMap.put(id, encodedBitmapData);
@@ -309,9 +322,10 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
   * fractions. In case of missing tts:extent the pixel defined regions can't be parsed, and null is
   * returned.
   */
+  @Nullable
  private TtmlRegion parseRegionAttributes(
-      XmlPullParser xmlParser, CellResolution cellResolution, TtsExtent ttsExtent) {
+      XmlPullParser xmlParser, CellResolution cellResolution, @Nullable TtsExtent ttsExtent) {
-    String regionId = XmlPullParserUtil.getAttributeValue(xmlParser, TtmlNode.ATTR_ID);
+    @Nullable String regionId = XmlPullParserUtil.getAttributeValue(xmlParser, TtmlNode.ATTR_ID);
    if (regionId == null) {
      return null;
    }
@@ -319,14 +333,16 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    float position;
    float line;
+    @Nullable
    String regionOrigin = XmlPullParserUtil.getAttributeValue(xmlParser, TtmlNode.ATTR_TTS_ORIGIN);
    if (regionOrigin != null) {
      Matcher originPercentageMatcher = PERCENTAGE_COORDINATES.matcher(regionOrigin);
      Matcher originPixelMatcher = PIXEL_COORDINATES.matcher(regionOrigin);
      if (originPercentageMatcher.matches()) {
        try {
-          position = Float.parseFloat(originPercentageMatcher.group(1)) / 100f;
+          position =
-          line = Float.parseFloat(originPercentageMatcher.group(2)) / 100f;
+              Float.parseFloat(Assertions.checkNotNull(originPercentageMatcher.group(1))) / 100f;
+          line = Float.parseFloat(Assertions.checkNotNull(originPercentageMatcher.group(2))) / 100f;
        } catch (NumberFormatException e) {
          Log.w(TAG, "Ignoring region with malformed origin: " + regionOrigin);
          return null;
@@ -337,8 +353,8 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
          return null;
        }
        try {
-          int width = Integer.parseInt(originPixelMatcher.group(1));
+          int width = Integer.parseInt(Assertions.checkNotNull(originPixelMatcher.group(1)));
-          int height = Integer.parseInt(originPixelMatcher.group(2));
+          int height = Integer.parseInt(Assertions.checkNotNull(originPixelMatcher.group(2)));
          // Convert pixel values to fractions.
          position = width / (float) ttsExtent.width;
          line = height / (float) ttsExtent.height;
@@ -362,14 +378,17 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    float width;
    float height;
+    @Nullable
    String regionExtent = XmlPullParserUtil.getAttributeValue(xmlParser, TtmlNode.ATTR_TTS_EXTENT);
    if (regionExtent != null) {
      Matcher extentPercentageMatcher = PERCENTAGE_COORDINATES.matcher(regionExtent);
      Matcher extentPixelMatcher = PIXEL_COORDINATES.matcher(regionExtent);
      if (extentPercentageMatcher.matches()) {
        try {
-          width = Float.parseFloat(extentPercentageMatcher.group(1)) / 100f;
+          width =
-          height = Float.parseFloat(extentPercentageMatcher.group(2)) / 100f;
+              Float.parseFloat(Assertions.checkNotNull(extentPercentageMatcher.group(1))) / 100f;
+          height =
+              Float.parseFloat(Assertions.checkNotNull(extentPercentageMatcher.group(2))) / 100f;
        } catch (NumberFormatException e) {
          Log.w(TAG, "Ignoring region with malformed extent: " + regionOrigin);
          return null;
@@ -380,8 +399,8 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
          return null;
        }
        try {
-          int extentWidth = Integer.parseInt(extentPixelMatcher.group(1));
+          int extentWidth = Integer.parseInt(Assertions.checkNotNull(extentPixelMatcher.group(1)));
-          int extentHeight = Integer.parseInt(extentPixelMatcher.group(2));
+          int extentHeight = Integer.parseInt(Assertions.checkNotNull(extentPixelMatcher.group(2)));
          // Convert pixel values to fractions.
          width = extentWidth / (float) ttsExtent.width;
          height = extentHeight / (float) ttsExtent.height;
@@ -404,8 +423,9 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    }
    @Cue.AnchorType int lineAnchor = Cue.ANCHOR_TYPE_START;
-    String displayAlign = XmlPullParserUtil.getAttributeValue(xmlParser,
+    @Nullable
-        TtmlNode.ATTR_TTS_DISPLAY_ALIGN);
+    String displayAlign =
+        XmlPullParserUtil.getAttributeValue(xmlParser, TtmlNode.ATTR_TTS_DISPLAY_ALIGN);
    if (displayAlign != null) {
      switch (Util.toLowerInvariant(displayAlign)) {
        case "center":
@@ -440,7 +460,8 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    return parentStyleIds.isEmpty() ? new String[0] : Util.split(parentStyleIds, "\\s+");
  }
-  private TtmlStyle parseStyleAttributes(XmlPullParser parser, TtmlStyle style) {
+  @PolyNull
+  private TtmlStyle parseStyleAttributes(XmlPullParser parser, @PolyNull TtmlStyle style) {
    int attributeCount = parser.getAttributeCount();
    for (int i = 0; i < attributeCount; i++) {
      String attributeValue = parser.getAttributeValue(i);
@@ -527,21 +548,24 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    return style;
  }
-  private TtmlStyle createIfNull(TtmlStyle style) {
+  private TtmlStyle createIfNull(@Nullable TtmlStyle style) {
    return style == null ? new TtmlStyle() : style;
  }
-  private TtmlNode parseNode(XmlPullParser parser, TtmlNode parent,
+  private TtmlNode parseNode(
-      Map<String, TtmlRegion> regionMap, FrameAndTickRate frameAndTickRate)
+      XmlPullParser parser,
+      @Nullable TtmlNode parent,
+      Map<String, TtmlRegion> regionMap,
+      FrameAndTickRate frameAndTickRate)
      throws SubtitleDecoderException {
    long duration = C.TIME_UNSET;
    long startTime = C.TIME_UNSET;
    long endTime = C.TIME_UNSET;
    String regionId = TtmlNode.ANONYMOUS_REGION_ID;
-    String imageId = null;
+    @Nullable String imageId = null;
-    String[] styleIds = null;
+    @Nullable String[] styleIds = null;
    int attributeCount = parser.getAttributeCount();
-    TtmlStyle style = parseStyleAttributes(parser, null);
+    @Nullable TtmlStyle style = parseStyleAttributes(parser, null);
    for (int i = 0; i < attributeCount; i++) {
      String attr = parser.getAttributeName(i);
      String value = parser.getAttributeValue(i);
@@ -636,7 +660,7 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    }
    if (matcher.matches()) {
-      String unit = matcher.group(3);
+      String unit = Assertions.checkNotNull(matcher.group(3));
      switch (unit) {
        case "px":
          out.setFontSizeUnit(TtmlStyle.FONT_SIZE_UNIT_PIXEL);
@@ -650,7 +674,7 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
        default:
          throw new SubtitleDecoderException("Invalid unit for fontSize: '" + unit + "'.");
      }
-      out.setFontSize(Float.valueOf(matcher.group(1)));
+      out.setFontSize(Float.parseFloat(Assertions.checkNotNull(matcher.group(1))));
    } else {
      throw new SubtitleDecoderException("Invalid expression for fontSize: '" + expression + "'.");
    }
@@ -671,18 +695,18 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
      throws SubtitleDecoderException {
    Matcher matcher = CLOCK_TIME.matcher(time);
    if (matcher.matches()) {
-      String hours = matcher.group(1);
+      String hours = Assertions.checkNotNull(matcher.group(1));
      double durationSeconds = Long.parseLong(hours) * 3600;
-      String minutes = matcher.group(2);
+      String minutes = Assertions.checkNotNull(matcher.group(2));
      durationSeconds += Long.parseLong(minutes) * 60;
-      String seconds = matcher.group(3);
+      String seconds = Assertions.checkNotNull(matcher.group(3));
      durationSeconds += Long.parseLong(seconds);
-      String fraction = matcher.group(4);
+      @Nullable String fraction = matcher.group(4);
      durationSeconds += (fraction != null) ? Double.parseDouble(fraction) : 0;
-      String frames = matcher.group(5);
+      @Nullable String frames = matcher.group(5);
      durationSeconds += (frames != null)
          ? Long.parseLong(frames) / frameAndTickRate.effectiveFrameRate : 0;
-      String subframes = matcher.group(6);
+      @Nullable String subframes = matcher.group(6);
      durationSeconds += (subframes != null)
          ? ((double) Long.parseLong(subframes)) / frameAndTickRate.subFrameRate
              / frameAndTickRate.effectiveFrameRate
@@ -691,9 +715,9 @@ public final class TtmlDecoder extends SimpleSubtitleDecoder {
    }
    matcher = OFFSET_TIME.matcher(time);
    if (matcher.matches()) {
-      String timeValue = matcher.group(1);
+      String timeValue = Assertions.checkNotNull(matcher.group(1));
      double offsetSeconds = Double.parseDouble(timeValue);
-      String unit = matcher.group(2);
+      String unit = Assertions.checkNotNull(matcher.group(2));
      switch (unit) {
        case "h":
          offsetSeconds *= 3600;

--- a/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlNode.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlNode.java
@@ -31,6 +31,7 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.TreeMap;
 import java.util.TreeSet;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 /**
 * A package internal representation of TTML node.
@@ -93,7 +94,7 @@ import java.util.TreeSet;
  private final HashMap<String, Integer> nodeStartsByRegion;
  private final HashMap<String, Integer> nodeEndsByRegion;
-  private List<TtmlNode> children;
+  @MonotonicNonNull private List<TtmlNode> children;
  public static TtmlNode buildTextNode(String text) {
    return new TtmlNode(
@@ -196,6 +197,7 @@ import java.util.TreeSet;
    }
  }
+  @Nullable
  public String[] getStyleIds() {
    return styleIds;
  }
@@ -217,7 +219,7 @@ import java.util.TreeSet;
    // Create image based cues.
    for (Pair<String, String> regionImagePair : regionImageOutputs) {
-      String encodedBitmapData = imageMap.get(regionImagePair.second);
+      @Nullable String encodedBitmapData = imageMap.get(regionImagePair.second);
      if (encodedBitmapData == null) {
        // Image reference points to an invalid image. Do nothing.
        continue;
@@ -225,7 +227,7 @@ import java.util.TreeSet;
      byte[] bitmapData = Base64.decode(encodedBitmapData, Base64.DEFAULT);
      Bitmap bitmap = BitmapFactory.decodeByteArray(bitmapData, /* offset= */ 0, bitmapData.length);
-      TtmlRegion region = regionMap.get(regionImagePair.first);
+      TtmlRegion region = Assertions.checkNotNull(regionMap.get(regionImagePair.first));
      cues.add(
          new Cue.Builder()
@@ -241,7 +243,7 @@ import java.util.TreeSet;
    // Create text based cues.
    for (Entry<String, SpannableStringBuilder> entry : regionTextOutputs.entrySet()) {
-      TtmlRegion region = regionMap.get(entry.getKey());
+      TtmlRegion region = Assertions.checkNotNull(regionMap.get(entry.getKey()));
      cues.add(
          new Cue(
              cleanUpText(entry.getValue()),
@@ -286,7 +288,7 @@ import java.util.TreeSet;
    String resolvedRegionId = ANONYMOUS_REGION_ID.equals(regionId) ? inheritedRegion : regionId;
    if (isTextNode && descendsPNode) {
-      getRegionOutput(resolvedRegionId, regionOutputs).append(text);
+      getRegionOutput(resolvedRegionId, regionOutputs).append(Assertions.checkNotNull(text));
    } else if (TAG_BR.equals(tag) && descendsPNode) {
      getRegionOutput(resolvedRegionId, regionOutputs).append('\n');
    } else if (isActive(timeUs)) {
@@ -330,7 +332,7 @@ import java.util.TreeSet;
      int start = nodeStartsByRegion.containsKey(regionId) ? nodeStartsByRegion.get(regionId) : 0;
      int end = entry.getValue();
      if (start != end) {
-        SpannableStringBuilder regionOutput = regionOutputs.get(regionId);
+        SpannableStringBuilder regionOutput = Assertions.checkNotNull(regionOutputs.get(regionId));
        applyStyleToOutput(globalStyles, regionOutput, start, end);
      }
    }
@@ -344,7 +346,7 @@ import java.util.TreeSet;
      SpannableStringBuilder regionOutput,
      int start,
      int end) {
-    TtmlStyle resolvedStyle = TtmlRenderUtil.resolveStyle(style, styleIds, globalStyles);
+    @Nullable TtmlStyle resolvedStyle = TtmlRenderUtil.resolveStyle(style, styleIds, globalStyles);
    if (resolvedStyle != null) {
      TtmlRenderUtil.applyStylesToSpan(regionOutput, start, end, resolvedStyle);
    }

--- a/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlRenderUtil.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlRenderUtil.java
@@ -15,6 +15,7 @@
 */
 package com.google.android.exoplayer2.text.ttml;
+import android.text.Layout.Alignment;
 import android.text.SpannableStringBuilder;
 import android.text.Spanned;
 import android.text.style.AbsoluteSizeSpan;
@@ -26,6 +27,7 @@ import android.text.style.StrikethroughSpan;
 import android.text.style.StyleSpan;
 import android.text.style.TypefaceSpan;
 import android.text.style.UnderlineSpan;
+import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.text.SpanUtil;
 import java.util.Map;
@@ -34,31 +36,36 @@ import java.util.Map;
 */
 /* package */ final class TtmlRenderUtil {
-  public static TtmlStyle resolveStyle(TtmlStyle style, String[] styleIds,
+  @Nullable
-      Map<String, TtmlStyle> globalStyles) {
+  public static TtmlStyle resolveStyle(
-    if (style == null && styleIds == null) {
+      @Nullable TtmlStyle style, @Nullable String[] styleIds, Map<String, TtmlStyle> globalStyles) {
+    if (style == null) {
+      if (styleIds == null) {
        // No styles at all.
        return null;
-    } else if (style == null && styleIds.length == 1) {
+      } else if (styleIds.length == 1) {
        // Only one single referential style present.
        return globalStyles.get(styleIds[0]);
-    } else if (style == null && styleIds.length > 1) {
+      } else if (styleIds.length > 1) {
        // Only multiple referential styles present.
        TtmlStyle chainedStyle = new TtmlStyle();
        for (String id : styleIds) {
          chainedStyle.chain(globalStyles.get(id));
        }
        return chainedStyle;
-    } else if (style != null && styleIds != null && styleIds.length == 1) {
+      }
+    } else /* style != null */ {
+      if (styleIds != null && styleIds.length == 1) {
        // Merge a single referential style into inline style.
        return style.chain(globalStyles.get(styleIds[0]));
-    } else if (style != null && styleIds != null && styleIds.length > 1) {
+      } else if (styleIds != null && styleIds.length > 1) {
        // Merge multiple referential styles into inline style.
        for (String id : styleIds) {
          style.chain(globalStyles.get(id));
        }
        return style;
      }
+    }
    // Only inline styles available.
    return style;
  }
@@ -100,10 +107,11 @@ import java.util.Map;
          end,
          Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
    }
-    if (style.getTextAlign() != null) {
+    @Nullable Alignment textAlign = style.getTextAlign();
+    if (textAlign != null) {
      SpanUtil.addOrReplaceSpan(
          builder,
-          new AlignmentSpan.Standard(style.getTextAlign()),
+          new AlignmentSpan.Standard(textAlign),
          start,
          end,
          Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);

--- a/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlStyle.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlStyle.java
@@ -18,9 +18,11 @@ package com.google.android.exoplayer2.text.ttml;
 import android.graphics.Typeface;
 import android.text.Layout;
 import androidx.annotation.IntDef;
+import androidx.annotation.Nullable;
 import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 /**
 * Style object of a <code>TtmlNode</code>
@@ -58,7 +60,7 @@ import java.lang.annotation.RetentionPolicy;
  private static final int OFF = 0;
  private static final int ON = 1;
-  private String fontFamily;
+  private @MonotonicNonNull String fontFamily;
  private int fontColor;
  private boolean hasFontColor;
  private int backgroundColor;
@@ -69,8 +71,8 @@ import java.lang.annotation.RetentionPolicy;
  @OptionalBoolean private int italic;
  @FontSizeUnit private int fontSizeUnit;
  private float fontSize;
-  private String id;
+  private @MonotonicNonNull String id;
-  private Layout.Alignment textAlign;
+  private Layout.@MonotonicNonNull Alignment textAlign;
  public TtmlStyle() {
    linethrough = UNSPECIFIED;
@@ -122,6 +124,7 @@ import java.lang.annotation.RetentionPolicy;
    return this;
  }
+  @Nullable
  public String getFontFamily() {
    return fontFamily;
  }
@@ -171,7 +174,7 @@ import java.lang.annotation.RetentionPolicy;
   *
   * @param ancestor the referential style to inherit from
   */
-  public TtmlStyle chain(TtmlStyle ancestor) {
+  public TtmlStyle chain(@Nullable TtmlStyle ancestor) {
    return inherit(ancestor, true);
  }
@@ -182,11 +185,11 @@ import java.lang.annotation.RetentionPolicy;
   *
   * @param ancestor the ancestor style to inherit from
   */
-  public TtmlStyle inherit(TtmlStyle ancestor) {
+  public TtmlStyle inherit(@Nullable TtmlStyle ancestor) {
    return inherit(ancestor, false);
  }
-  private TtmlStyle inherit(TtmlStyle ancestor, boolean chaining) {
+  private TtmlStyle inherit(@Nullable TtmlStyle ancestor, boolean chaining) {
    if (ancestor != null) {
      if (!hasFontColor && ancestor.hasFontColor) {
        setFontColor(ancestor.fontColor);
@@ -197,7 +200,7 @@ import java.lang.annotation.RetentionPolicy;
      if (italic == UNSPECIFIED) {
        italic = ancestor.italic;
      }
-      if (fontFamily == null) {
+      if (fontFamily == null && ancestor.fontFamily != null) {
        fontFamily = ancestor.fontFamily;
      }
      if (linethrough == UNSPECIFIED) {
@@ -206,7 +209,7 @@ import java.lang.annotation.RetentionPolicy;
      if (underline == UNSPECIFIED) {
        underline = ancestor.underline;
      }
-      if (textAlign == null) {
+      if (textAlign == null && ancestor.textAlign != null) {
        textAlign = ancestor.textAlign;
      }
      if (fontSizeUnit == UNSPECIFIED) {
@@ -226,10 +229,12 @@ import java.lang.annotation.RetentionPolicy;
    return this;
  }
+  @Nullable
  public String getId() {
    return id;
  }
+  @Nullable
  public Layout.Alignment getTextAlign() {
    return textAlign;
  }