fixed check for missing fields

Author: tclose

pydra/engine/specs.py

@@ -509,7 +509,7 @@ def _check_rules(self):
 
             # Raise error if any required field is unset.
             if (
-                value
+                (value is None or value is False)
                 and field.requires
                 and not any(rs.satisfied(self) for rs in field.requires)
             ):