checkNotNull

core/src/main/java/io/grpc/internal/ManagedChannelImplBuilder.java

@@ -621,7 +621,7 @@ public <X> ManagedChannelImplBuilder setNameResolverArg(NameResolver.Args.Key<X>
     if (nameResolverCustomArgs == null) {
       nameResolverCustomArgs = new IdentityHashMap<>();
     }
-    nameResolverCustomArgs.put(key, value);
+    nameResolverCustomArgs.put(checkNotNull(key, "key"), checkNotNull(value, "value"));
     return this;
   }