fix g.parser to support also G_OPT_M_NULL_VALUE

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@63175 15284696-431f-4ddb-bdfa-cd5b030d7da7

general/g.parser/standard_option.c

@@ -59,6 +59,7 @@ static char* STD_OPT_STRINGS[] = {"G_OPT_UNDEFINED",
                                   "G_OPT_M_COLR",
                                   "G_OPT_M_DIR",
                                   "G_OPT_M_REGION",
+                                  "G_OPT_M_NULL_VALUE",
                                   "G_OPT_STDS_INPUT",
                                   "G_OPT_STDS_INPUTS",
                                   "G_OPT_STDS_OUTPUT",