Fatal error: Uncaught Error: Call to a member function query() on null after upgrading to PHP 8.0

The error message Fatal error: Uncaught Error: Call to a member function query() on null indicates that you are trying to call the query() method on an object that is null, meaning it does not have a value assigned. This typically occurs when the object that you are trying to call the method on was not properly instantiated or created.

Here are a few common reasons for this error:

Incomplete class definition:

If you are using a class-based approach and the class definition is missing the method query(), you will get this error. Make sure that the class definition is complete and that the method query() is defined.

Incorrect instantiation:

If you are instantiating an object and passing the wrong parameters, the object may not be created properly and will not have the method query(). Check your instantiation code to ensure that you are passing the correct parameters.

Deprecated function:

If you were using a function that was deprecated in PHP 8.0, you may have to replace it with a different function. The method query() may have been deprecated in PHP 8.0 and replaced with a different method.

Incompatible library or extension:

If you are using an external library or extension that is not compatible with PHP 8.0, you may get this error. Make sure that all libraries and extensions that you are using are compatible with PHP 8.0.

To resolve this issue, you will need to carefully examine your code and make any necessary changes to fix the issue.