@Nullable
 private static PsiElement resolveDecorator(@NotNull PyDecorator decorator) {
   final PyExpression callee = decorator.getCallee();
   if (callee == null) {
     return null;
   }
   final PsiReference reference = callee.getReference();
   if (reference == null) {
     return null;
   }
   return reference.resolve();
 }