diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 3c695c1..95f36b8 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -8959,7 +8959,10 @@ estimate_variable_size(struct config_generic * gconf)
 			{
 				struct config_string *conf = (struct config_string *) gconf;
 
-				valsize = strlen(*conf->variable);
+				if (*conf->variable && **conf->variable)
+					valsize = strlen(*conf->variable);
+				else
+					valsize = 0;
 			}
 			break;
 
@@ -9109,7 +9112,9 @@ serialize_variable(char **destptr, Size *maxbytes,
 			{
 				struct config_string *conf = (struct config_string *) gconf;
 
-				do_serialize(destptr, maxbytes, "%s", *conf->variable);
+				do_serialize(destptr, maxbytes, "%s",
+							 *conf->variable && **conf->variable ?
+							 *conf->variable : "");
 			}
 			break;