added guard against missing implicit helps in custom compose packages

Author: tclose

pydra/compose/base/helpers.py

@@ -66,7 +66,7 @@ def ensure_field_objects(
                 )
             else:
                 arg.name = input_name
-            if not arg.help:
+            if not arg.help and input_helps:
                 arg.help = input_helps.get(input_name, "")
         elif is_type(arg):
             inputs[input_name] = arg_type(
@@ -100,7 +100,7 @@ def ensure_field_objects(
                 )
             else:
                 out.name = output_name
-            if not out.help:
+            if not out.help and output_helps:
                 out.help = output_helps.get(output_name, "")
         elif is_type(out):
             outputs[output_name] = out_type(