Check for a null set of binders.

(implicitly fixed by
I738fa4b2fe5cbb3a741ee85884eb02e13d3e85c5 though
it seems we'd rather be explicit/defensive).

Bug: 13331451
Change-Id: Id92382a5524ea33dc272d14820c4650941c8f7b3
diff --git a/src/com/android/telecomm/BinderDeallocator.java b/src/com/android/telecomm/BinderDeallocator.java
index ae62ec3..fc57158 100644
--- a/src/com/android/telecomm/BinderDeallocator.java
+++ b/src/com/android/telecomm/BinderDeallocator.java
@@ -87,7 +87,9 @@
     void updateBinders(Set<? extends ServiceBinder> binders) {
         ThreadUtil.checkOnMainThread();
 
-        mBinders.addAll(binders);
+        if (binders != null) {
+            mBinders.addAll(binders);
+        }
     }
 
     /**