Key error when target doesnt exist

I introduced target keywords to a lot of processing functions explicitly, to just realize a shortcut for copy(field, targt) + process(target) combo. There for, those unctions generate target fields.

Currently, register seems to check for targets existence, before calling the function, and thus, fails.

Traceback (most recent call last):
  File "/snap/pycharm-community/256/plugins/python-ce/helpers/pydev/_pydevd_bundle/pydevd_exec2.py", line 3, in Exec
    exec(exp, global_vars, local_vars)
  File "<string>", line 3, in <module>
  File "/home/luenensc/PyPojects/saqc/saqc/core/modules/drift.py", line 76, in correctDrift
    return self._defer("correctDrift", locals())
  File "/home/luenensc/PyPojects/saqc/saqc/core/modules/__init__.py", line 45, in _defer
    return self._wrap(FUNC_MAP[fname])(**flocals, **fkwargs)
  File "/home/luenensc/PyPojects/saqc/saqc/core/core.py", line 244, in inner
    **kwargs,
  File "/home/luenensc/PyPojects/saqc/saqc/core/core.py", line 260, in _callFunction
    data, flags = function(data=data, flags=flags, field=field, *args, **kwargs)
  File "/home/luenensc/PyPojects/saqc/saqc/core/register.py", line 113, in __call__
    self.data, self.flags, columns, self.mask_thresh
  File "/home/luenensc/PyPojects/saqc/saqc/core/register.py", line 298, in _maskData
    col_mask = _isflagged(flags[c].to_numpy(), thresh)
  File "/home/luenensc/PyPojects/saqc/saqc/core/flags.py", line 288, in __getitem__
    return self._data[key].max()
KeyError: 'sac254_corr'