presence: add client nil error

Author: tulir

presence.go

@@ -62,7 +62,9 @@ func (cli *Client) handlePresence(node *waBinary.Node) {
 // You should call this at least once after connecting so that the server has your pushname.
 // Otherwise, other users will see "-" as the name.
 func (cli *Client) SendPresence(state types.Presence) error {
-	if len(cli.Store.PushName) == 0 {
+	if cli == nil {
+		return ErrClientIsNil
+	} else if len(cli.Store.PushName) == 0 {
 		return ErrNoPushName
 	}
 	if state == types.PresenceAvailable {
@@ -88,6 +90,9 @@ func (cli *Client) SendPresence(state types.Presence) error {
 //
 //	cli.SendPresence(types.PresenceAvailable)
 func (cli *Client) SubscribePresence(jid types.JID) error {
+	if cli == nil {
+		return ErrClientIsNil
+	}
 	privacyToken, err := cli.Store.PrivacyTokens.GetPrivacyToken(context.TODO(), jid)
 	if err != nil {
 		return fmt.Errorf("failed to get privacy token: %w", err)