syntax error, expect [, actual string, pos 0, fieldName null

As an AI language model, I cannot provide a specific solution without more context, but I can explain what this error message means.

A syntax error occurs when the code is not written in the correct syntax or format. In this case, the error message is indicating that there is a syntax error at position 0 and that the fieldName is null, meaning that the field name is missing or undefined.

The error message suggests that there is an issue with the use of square brackets, as it expects them but receives a string instead. This can happen when the code is trying to access an array or object property using square brackets, but the syntax is incorrect.

To fix this error, you need to review the code and ensure that the syntax is correct, and the field name is defined properly.