diff --git a/src/common/iBatteryPlugin.vala b/src/common/iBatteryPlugin.vala
index a4b3502..5514cc3 100644
--- a/src/common/iBatteryPlugin.vala
+++ b/src/common/iBatteryPlugin.vala
@@ -76,7 +76,7 @@ namespace IndicatorKDEConnect {
         }
 
         protected void int32_signal_cb (DBusConnection con, 
-                                        string sender, 
+                                        string? sender,
                                         string object,
                                         string interface, 
                                         string signal_name, 
@@ -87,7 +87,7 @@ namespace IndicatorKDEConnect {
         }
 
         protected void boolean_signal_cb (DBusConnection con,
-                                          string sender,
+                                          string? sender,
                                           string object,
                                           string interface,
                                           string signal_name,
diff --git a/src/common/iDaemonPlugin.vala b/src/common/iDaemonPlugin.vala
index 8653729..201da90 100644
--- a/src/common/iDaemonPlugin.vala
+++ b/src/common/iDaemonPlugin.vala
@@ -114,7 +114,7 @@ namespace IndicatorKDEConnect {
         /*Signals Callbacks*/
 
         protected virtual void device_added_cb (DBusConnection con, 
-                                             string sender, 
+                                             string? sender,
                                              string object,
                                              string interface, 
                                              string signal_name, 
@@ -128,7 +128,7 @@ namespace IndicatorKDEConnect {
         }
 
         protected virtual void device_removed_cb (DBusConnection con, 
-                                               string sender, 
+                                               string? sender,
                                                string object,
                                                string interface, 
                                                string signal_name, 
@@ -142,7 +142,7 @@ namespace IndicatorKDEConnect {
         }
 
         protected virtual void device_visibility_changed_cb (DBusConnection con,
-                                                             string sender, 
+                                                             string? sender,
                                                              string object,
                                                              string interface, 
                                                              string signal_name, 
@@ -157,7 +157,7 @@ namespace IndicatorKDEConnect {
         }
 
         protected virtual void pairing_requests_changed_cb (DBusConnection con, 
-                                                         string sender, 
+                                                         string? sender,
                                                          string object,
                                                          string interface, 
                                                          string signal_name, 
diff --git a/src/common/iDevicePlugin.vala b/src/common/iDevicePlugin.vala
index 8570775..bad3eac 100644
--- a/src/common/iDevicePlugin.vala
+++ b/src/common/iDevicePlugin.vala
@@ -237,7 +237,7 @@ namespace IndicatorKDEConnect {
 
         /*Callbacks */
         protected void void_signal_cb (DBusConnection con, 
-                                       string sender,
+                                       string? sender,
                                        string object,
                                        string interface,
                                        string signal_name,
@@ -253,7 +253,7 @@ namespace IndicatorKDEConnect {
         }        
 
         protected void string_signal_cb (DBusConnection con, 
-                                         string sender,
+                                         string? sender,
                                          string object,
                                          string interface,
                                          string signal_name,
@@ -273,7 +273,7 @@ namespace IndicatorKDEConnect {
         }
 
         protected void boolean_signal_cb (DBusConnection con, 
-                                          string sender,
+                                          string? sender,
                                           string object,
                                           string interface,
                                           string signal_name,
diff --git a/src/common/iSignals.vala b/src/common/iSignals.vala
index 52c2b82..1eb390b 100644
--- a/src/common/iSignals.vala
+++ b/src/common/iSignals.vala
@@ -6,7 +6,7 @@
 namespace IndicatorKDEConnect {
     public interface ISignals : Object {
         public virtual void void_signal_cb (DBusConnection con, 
-                                            string sender, 
+                                            string? sender,
                                             string object,
                                             string interface, 
                                             string signal_name, 
@@ -16,7 +16,7 @@ namespace IndicatorKDEConnect {
         }
 
         public virtual void boolean_signal_cb (DBusConnection con, 
-                                               string sender,
+                                               string? sender,
                                                string object,
                                                string interface,
                                                string signal_name,
@@ -26,7 +26,7 @@ namespace IndicatorKDEConnect {
         }
 
         public virtual void string_signal_cb (DBusConnection con, 
-                                              string sender,
+                                              string? sender,
                                               string object,
                                               string interface,
                                               string signal_name,
@@ -36,7 +36,7 @@ namespace IndicatorKDEConnect {
         }                               
         
         public virtual void int32_signal_cb (DBusConnection con, 
-                                             string sender, 
+                                             string? sender,
                                              string object,
                                              string interface, 
                                              string signal_name, 
-- 
2.30.1