Add @Nullable for Retransmitter in BusyState

Bug: 222362041
Test: atest FrameworksIkeTests
Change-Id: Ife41ef75d72b6a75f2af2d99e717d6e9dc21b26c
diff --git a/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java b/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java
index e4ba5d8..adc8f49 100644
--- a/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java
+++ b/src/java/com/android/internal/net/ipsec/ike/IkeSessionStateMachine.java
@@ -1890,7 +1890,7 @@
      * IKE packet. Idle state will defer the received packet to a BusyState to process it.
      */
     private abstract class BusyState extends LocalRequestQueuer {
-        protected Retransmitter mRetransmitter;
+        @Nullable protected Retransmitter mRetransmitter;
 
         @Override
         public boolean processStateMessage(Message message) {