private void checkNulls(PsiType type, PsiExpression expression, String declaration) {
        if (expression != null && TypeUtils.isOptional(type)) {
          ExpressionUtils.nonStructuralChildren(expression).filter(ExpressionUtils::isNullLiteral)
            .forEach(nullLiteral -> register(nullLiteral, (PsiClassType)type, declaration));
        }
      }
private void checkNulls(PsiType type, PsiExpression expression, String declaration)