pymodbus cannot unpack non-iterable NoneType object

This error message typically indicates that the variable being unpacked is None, meaning that it has no value assigned to it. This can happen when a function or method that is expected to return a value fails to do so, or when a variable is not properly initialized before being used in a function or method.

To fix this error, make sure that any functions or methods that are expected to return a value actually do so, and that any variables used in these functions or methods are properly initialized beforehand. You may also need to add error handling code to catch cases where a variable is None and handle them appropriately