Check for null listeners in deprecated paths in DefaultDrmSessionManager.

The previous API allowed to pass in null to the constructors although variants
without listeners exist. That's why we need to handle these null values.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191577891

library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java

@@ -121,7 +121,9 @@ public class DefaultDrmSessionManager<T extends ExoMediaCrypto> implements DrmSe
       throws UnsupportedDrmException {
       throws UnsupportedDrmException {
     DefaultDrmSessionManager<FrameworkMediaCrypto> drmSessionManager =
     DefaultDrmSessionManager<FrameworkMediaCrypto> drmSessionManager =
         newWidevineInstance(callback, optionalKeyRequestParameters);
         newWidevineInstance(callback, optionalKeyRequestParameters);
-    drmSessionManager.addListener(eventHandler, eventListener);
+    if (eventHandler != null && eventListener != null) {
+      drmSessionManager.addListener(eventHandler, eventListener);
+    }
     return drmSessionManager;
     return drmSessionManager;
   }
   }
 
 
@@ -152,7 +154,9 @@ public class DefaultDrmSessionManager<T extends ExoMediaCrypto> implements DrmSe
       throws UnsupportedDrmException {
       throws UnsupportedDrmException {
     DefaultDrmSessionManager<FrameworkMediaCrypto> drmSessionManager =
     DefaultDrmSessionManager<FrameworkMediaCrypto> drmSessionManager =
         newPlayReadyInstance(callback, customData);
         newPlayReadyInstance(callback, customData);
-    drmSessionManager.addListener(eventHandler, eventListener);
+    if (eventHandler != null && eventListener != null) {
+      drmSessionManager.addListener(eventHandler, eventListener);
+    }
     return drmSessionManager;
     return drmSessionManager;
   }
   }
 
 
@@ -192,7 +196,9 @@ public class DefaultDrmSessionManager<T extends ExoMediaCrypto> implements DrmSe
       throws UnsupportedDrmException {
       throws UnsupportedDrmException {
     DefaultDrmSessionManager<FrameworkMediaCrypto> drmSessionManager =
     DefaultDrmSessionManager<FrameworkMediaCrypto> drmSessionManager =
         newFrameworkInstance(uuid, callback, optionalKeyRequestParameters);
         newFrameworkInstance(uuid, callback, optionalKeyRequestParameters);
-    drmSessionManager.addListener(eventHandler, eventListener);
+    if (eventHandler != null && eventListener != null) {
+      drmSessionManager.addListener(eventHandler, eventListener);
+    }
     return drmSessionManager;
     return drmSessionManager;
   }
   }
 
 
@@ -230,7 +236,9 @@ public class DefaultDrmSessionManager<T extends ExoMediaCrypto> implements DrmSe
       Handler eventHandler,
       Handler eventHandler,
       DefaultDrmSessionEventListener eventListener) {
       DefaultDrmSessionEventListener eventListener) {
     this(uuid, mediaDrm, callback, optionalKeyRequestParameters);
     this(uuid, mediaDrm, callback, optionalKeyRequestParameters);
-    addListener(eventHandler, eventListener);
+    if (eventHandler != null && eventListener != null) {
+      addListener(eventHandler, eventListener);
+    }
   }
   }
 
 
   /**
   /**
@@ -268,7 +276,9 @@ public class DefaultDrmSessionManager<T extends ExoMediaCrypto> implements DrmSe
       DefaultDrmSessionEventListener eventListener,
       DefaultDrmSessionEventListener eventListener,
       boolean multiSession) {
       boolean multiSession) {
     this(uuid, mediaDrm, callback, optionalKeyRequestParameters, multiSession);
     this(uuid, mediaDrm, callback, optionalKeyRequestParameters, multiSession);
-    addListener(eventHandler, eventListener);
+    if (eventHandler != null && eventListener != null) {
+      addListener(eventHandler, eventListener);
+    }
   }
   }
 
 
   /**
   /**
@@ -316,7 +326,9 @@ public class DefaultDrmSessionManager<T extends ExoMediaCrypto> implements DrmSe
         optionalKeyRequestParameters,
         optionalKeyRequestParameters,
         multiSession,
         multiSession,
         initialDrmRequestRetryCount);
         initialDrmRequestRetryCount);
-    addListener(eventHandler, eventListener);
+    if (eventHandler != null && eventListener != null) {
+      addListener(eventHandler, eventListener);
+    }
   }
   }
 
 
   /**
   /**