message: Avoid ignored exception in SessionRelease.
diff: @@ -474,6 +474,13 @@ Status SessionRef::RunCallable(CallableHandle handle,
  }
  Status SessionRef::ReleaseCallable(CallableHandle handle) {
  + {
  + mutex_lock l(run_lock_);
  + if (session_ == nullptr) {
  + // Session already closed. Do nothing.
  + return Status::OK();
  + }
  + }
  LOG_AND_RUN_OPERATION(ReleaseCallable, handle);
  }
  