It doesn’t have a `@flow` annotation. We should start Flow-ifying it to avoid bugs like https://github.com/facebook/react/pull/11173.

@iamdustan Wanna take it?
var content = '';
  
  
  React.Children.forEach(children, function(child) {
    if (child == null) {
      return;
    }
    if (typeof child === 'string' || typeof child === 'number') {
      content += child;
    } else {
      if (__DEV__) {
        if (!didWarnInvalidOptionChildren) {
          didWarnInvalidOptionChildren = true;
          warning(
            false,
            'Only strings and numbers are supported as <option> children.',
          );
        }
      }
    }
  });
  return content;
}
function maskContext(type, context) {