Add characteristics initial values

Sets default values for characteristics if not specified explicitly

bumble/profiles/gmap.py

@@ -78,10 +78,10 @@ class GamingAudioService(TemplateService):
     UUID = GATT_GAMING_AUDIO_SERVICE
 
     gmap_role: Characteristic
-    ugg_features: Optional[Characteristic]
-    ugt_features: Optional[Characteristic]
-    bgs_features: Optional[Characteristic]
-    bgr_features: Optional[Characteristic]
+    ugg_features: Optional[Characteristic] = None
+    ugt_features: Optional[Characteristic] = None
+    bgs_features: Optional[Characteristic] = None
+    bgr_features: Optional[Characteristic] = None
 
     def __init__(
         self,
@@ -93,6 +93,11 @@ def __init__(
     ) -> None:
         characteristics = []
 
+        ugg_features = UggFeatures(0) if ugg_features is None else ugg_features
+        ugt_features = UgtFeatures(0) if ugt_features is None else ugt_features
+        bgs_features = BgsFeatures(0) if bgs_features is None else bgs_features
+        bgr_features = BgrFeatures(0) if bgr_features is None else bgr_features
+
         self.gmap_role = Characteristic(
             uuid=GATT_GMAP_ROLE_CHARACTERISTIC,
             properties=Characteristic.Properties.READ,