public @Nullable <T> T findChildByClass(Class<T> aClass) {
    for (PsiElement child : getChildren()) {
      if (aClass.isInstance(child)) {
        //noinspection unchecked
        return (T)child;
      }
    }
    return null;
  }
public @Nullable <T> T findChildByClass(Class<T> aClass)