Fixed some bugs in placeholder

PLACEHOLDERS.md

@@ -14,7 +14,7 @@ Actions
 
 | Action Name | Description |
 | --- | --- |
-| player | Playing status. |
+| play | Playing status. |
 | listen | Listening status. |
 | watch | Watching status. |
 | stream | Streaming status. |

addons/placeholders.py

@@ -34,9 +34,7 @@ class Placeholders:
 
         for key in keys:
             value = self.variables.get(key.lower(), None)
-            if value is None:
-                continue
-
-            msg = msg.replace(f"@@{key}@@", str(value()))
+            if value:
+                msg = msg.replace(f"@@{key}@@", str(value()))
 
         return msg