fix: reverted fix while keeping changed meta tag.

@bpinsard - reverting the fix while keeping name source. too many doctests started failing. the intent of spec.genfile or spec.name_source is when the input is undefined, not when its defined.

Author: satra

nipype/interfaces/base.py

@@ -1391,11 +1391,11 @@ def _parse_inputs(self, skip=None):
             if skip and name in skip:
                 continue
             value = getattr(self.inputs, name)
-            if spec.genfile or spec.name_source:
-                if isdefined(value):
-                    value = self._gen_filename(name)
             if not isdefined(value):
-                continue
+                if spec.genfile or spec.name_source:
+                    value = self._gen_filename(name)
+                else:
+                    continue
             arg = self._format_arg(name, spec, value)
             if arg is None:
                 continue