Looks like the test added in this patch is racy, it failed for me after I looped it for a couple minutes. When System.gc returns it just means the gc has made a best effort to run, not that it actually has, so in the cases where the gc hasn't run the test will fail because myArg was not reaped.
The change itself looks correct. Since this is a one-liner and memory leaks like this are hard to test I'd be OK with a new patch that just fixes the bug as long as it passes the existing RPC tests. Any other suggestions on how to add test coverage of course are welcome, doesn't seem worth eg adding a getter that returns the number of calls.