expand the returns to included the case for None

mpsd-software-environment.py

@@ -58,7 +58,7 @@ def create_log_file_names(
     action: str,
     date: str = call_date_iso,
     toolchain: str = None,
-) -> str:
+) -> Union[str, None]:
     """Create log file names.
 
     This function creates the log file names for either the installer or
@@ -86,10 +86,12 @@ def create_log_file_names(
 
     Returns
     -------
-    str
+    str or None
         log file name
         installer_log_file_name or build_log_file_name depending on the
         parameters given.
+        If the action is not one that changes the files on disk ( info only actions)
+        then None is returned.
     """
     if toolchain:
         # if toolchain is given, then  we build the build_log_file_name