Add more info to Preconditions check
@@ -305,7 +305,7 @@ class FunctionInjector {
newExpression = NodeUtil.newUndefinedNode(srcLocation);
} else {
Node returnNode = block.getFirstChild();
- checkArgument(returnNode.isReturn());
+ checkArgument(returnNode.isReturn(), returnNode);
// Clone the return node first.
Node safeReturnNode = returnNode.cloneTree();
