Remove Nullable annotation

Change-Id: I06e9909e0a813aecccae4e0f4fb233b0049c2a93
diff --git a/src/main/java/com/android/tools/r8/utils/collections/ThrowingMap.java b/src/main/java/com/android/tools/r8/utils/collections/ThrowingMap.java
index bc85834..46473f1 100644
--- a/src/main/java/com/android/tools/r8/utils/collections/ThrowingMap.java
+++ b/src/main/java/com/android/tools/r8/utils/collections/ThrowingMap.java
@@ -8,7 +8,6 @@
 import java.util.Collection;
 import java.util.Map;
 import java.util.Set;
-import org.jetbrains.annotations.Nullable;
 
 public class ThrowingMap<K, V> implements Map<K, V> {
 
@@ -60,7 +59,6 @@
     throw new Unreachable();
   }
 
-  @Nullable
   @Override
   public V put(K key, V value) {
     throw new Unreachable();