Allow metadata values to be "", after all, its versioned.

sql/database-fill.sql

@@ -809,7 +809,7 @@ REPLACE INTO table_regex VALUES ('archive_tags','tag','text','regex','^[a-zA-Z][
 REPLACE INTO table_regex VALUES ('experiment_templates','description','text','regex','^[\\040-\\176\\012\\015\\011]*$',1,4096,NULL);
 REPLACE INTO table_regex VALUES ('experiment_templates','guid','text','regex','^[\\w]+$',1,32,NULL);
 REPLACE INTO table_regex VALUES ('experiment_template_metadata','name','text','regex','^[\\040-\\176]*$',1,64,NULL);
-REPLACE INTO table_regex VALUES ('experiment_template_metadata','value','text','regex','^[\\040-\\176\\012\\015\\011]*$',1,2048,NULL);
+REPLACE INTO table_regex VALUES ('experiment_template_metadata','value','text','regex','^[\\040-\\176\\012\\015\\011]*$',0,4096,NULL);
 REPLACE INTO table_regex VALUES ('experiment_template_metadata','metadata_type','text','regex','^[\\w]*$',1,64,NULL);
 REPLACE INTO table_regex VALUES ('virt_parameters','pid','text','redirect','projects:pid',0,0,NULL);
 REPLACE INTO table_regex VALUES ('virt_parameters','eid','text','redirect','experiments:eid',0,0,NULL);