def DEFAULT_NULLVALUEFORMAT(format):
return <NUM_LIT:0> if format.startswith(('<STR_LIT>','<STR_LIT>'))else <NUM_LIT:0.0> if format.startswith('<STR_LIT>')else '<STR_LIT>'<EOL>
Returns a null value for each of the various kinds of numpy formats.

Default null value function used in :func:`tabular.spreadsheet.join`.

**Parameters**

        **format** :  string

                Numpy format descriptor, e.g. ``'<i4'``, ``'|S5'``.

**Returns**

        **null** :  element in `[0, 0.0, '']`

                Null value corresponding to the given format:

                *   if ``format.startswith(('<i', '|b'))``, e.g. `format`
                    corresponds to an integer or Boolean, return 0

                *   else if `format.startswith('<f')`, e.g. `format`
                    corresponds to a float, return 0.0

                *   else, e.g. `format` corresponds to a string, return ''