fix #1244

conventional.yaml

         # users to do session resumption / query history after disconnections.
         grace-period: 1h
 
-    # options to store history messages in a persistent database (currently only MySQL):
+    # options to store history messages in a persistent database (currently only MySQL).
+    # in order to enable any of this functionality, you must configure a MySQL server
+    # in the `datastore.mysql` section.
     persistent:
         enabled: false
 

default.yaml

         # users to do session resumption / query history after disconnections.
         grace-period: 1h
 
-    # options to store history messages in a persistent database (currently only MySQL):
+    # options to store history messages in a persistent database (currently only MySQL).
+    # in order to enable any of this functionality, you must configure a MySQL server
+    # in the `datastore.mysql` section.
     persistent:
         enabled: false
 

irc/config.go

 	}
 
 	if !config.History.Enabled || !config.History.Persistent.Enabled {
+		config.History.Persistent.Enabled = false
 		config.History.Persistent.UnregisteredChannels = false
 		config.History.Persistent.RegisteredChannels = PersistentDisabled
 		config.History.Persistent.DirectMessages = PersistentDisabled
 	}
 
+	if config.History.Persistent.Enabled && !config.Datastore.MySQL.Enabled {
+		return nil, fmt.Errorf("You must configure a MySQL server in order to enable persistent history")
+	}
+
 	if config.History.ZNCMax == 0 {
 		config.History.ZNCMax = config.History.ChathistoryMax
 	}