message: Don't check for if null after already dereferenced
  I'm not sure how it could be null at this point (and obviously it is nowhere else we'd have seen failures), but keeping the check as is and just moving it to where it would catch it before dereferencing.
diff: @@ -55,11 +55,13 @@ Status FunctionDefToBodyHelper(
  const StackTracesMap& stack_traces =
  lib_def->GetStackTraces(fdef.signature().name());
  for (Node* n : graph->nodes()) {
  + if (n) {
  auto it = stack_traces.find(n->name());
  - if (n && it != stack_traces.end()) {
  + if (it != stack_traces.end()) {
  n->SetStackTrace(it->second);
  }
  }
  + }
  // Call BuildControlFlowInfo to validate that this function body has
  // well-formed control flow.
  