private boolean isReferenceToNullableVariable(
      PsiExpression lhs) {
      if (!(lhs instanceof PsiReferenceExpression referenceExpression)) {
        return false;
      }
      final PsiElement element = referenceExpression.resolve();
      if (!(element instanceof PsiVariable variable)) {
        return false;
      }
      if (ignoreAssignmentsToFields && variable instanceof PsiField) {
        return true;
      }
      return NullableNotNullManager.isNullable(variable);
    }
private boolean isReferenceToNullableVariable(
      PsiExpression lhs)