refactor: deprecate redundant non-null on user agent

Author: yhkee0404

app/src/main/java/dev/bluehouse/enablevolte/Moder.kt

@@ -466,8 +466,8 @@ class SubscriptionModer(
                 false
             }
 
-    val userAgentConfig: String
-        get() = this.getStringValue(KEY_IMS_USER_AGENT) ?: ""
+    val userAgentConfig: String?
+        get() = this.getStringValue(KEY_IMS_USER_AGENT)
 
     val isIMSRegistered: Boolean
         get() {

app/src/main/java/dev/bluehouse/enablevolte/pages/Config.kt

@@ -111,12 +111,7 @@ fun Config(
         show4GForLteEnabled = VERSION.SDK_INT >= VERSION_CODES.R && moder.isShow4GForLteEnabled
         hideEnhancedDataIconEnabled = VERSION.SDK_INT >= VERSION_CODES.R && moder.isHideEnhancedDataIconEnabled
         is4GPlusEnabled = moder.is4GPlusEnabled
-        configuredUserAgent =
-            try {
-                moder.userAgentConfig
-            } catch (e: java.lang.NullPointerException) {
-                null
-            }
+        configuredUserAgent = moder.userAgentConfig
     }
 
     LaunchedEffect(true) {