Another error that can arise from a migrate is this:
AttributeError: ‘NoneType’ object has no attribute ‘options’
Often the fix is to run bench reload-doc (or Update as above that performs the same function).
To know what particular DocType to reload, it helps to see the full traceback. To learn the module where the DocType resides one can grep the code.
Here’s an example case [v12] Can't send Documents via Email after upgrading to v12 - #4 by jignesh_shah