Never use null collections

Don't null out collections; clear() them instead.

Change-Id: I738fa4b2fe5cbb3a741ee85884eb02e13d3e85c5
diff --git a/src/com/android/telecomm/OutgoingCallProcessor.java b/src/com/android/telecomm/OutgoingCallProcessor.java
index a0875c9..aa0a0bb 100644
--- a/src/com/android/telecomm/OutgoingCallProcessor.java
+++ b/src/com/android/telecomm/OutgoingCallProcessor.java
@@ -269,7 +269,7 @@
             return;
         }
 
-        if (mCallServiceDescriptorIterator.hasNext()) {
+        if (mCallServiceDescriptorIterator != null && mCallServiceDescriptorIterator.hasNext()) {
             CallServiceDescriptor descriptor = mCallServiceDescriptorIterator.next();
             final CallServiceWrapper callService =
                     mCallServicesById.get(descriptor.getCallServiceId());