Error: Unable to handle function call in Cloud Functions Firestore - flutter

Question

I want to receive the document form current user uid passed at client side. I tried it using functions.onRequest and successfully got the result but I got the error that while using onCall method.
Cloud Function
exports.getUserData = functions.https.onCall((data) => {
const test = data.text;
db.collection('users').doc(test).get().then((value)=>{
return value.data();
}).catch((e)=>{
return ("Error in CFunction"+e);
})
});
Client-side Call
Future _callable()async{
FirebaseUser currentUser = await _auth.currentUser();
final uid = currentUser.uid;
final HttpsCallable callable =
CloudFunctions.instance.getHttpsCallable(functionName: 'getUserData');
var data = await callable.call(uid);
print(data.data);
}
Error I am getting
E/MethodChannel#cloud_functions(12458): Failed to handle method call
E/MethodChannel#cloud_functions(12458): java.lang.ClassCastException: java.lang.String cannot be cast to java.util.Map
E/MethodChannel#cloud_functions(12458): at io.flutter.plugins.firebase.cloudfunctions.CloudFunctionsPlugin.onMethodCall(CloudFunctionsPlugin.java:37)
E/MethodChannel#cloud_functions(12458): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:226)
E/MethodChannel#cloud_functions(12458): at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:85)
E/MethodChannel#cloud_functions(12458): at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:631)
E/MethodChannel#cloud_functions(12458): at android.os.MessageQueue.nativePollOnce(Native Method)
E/MethodChannel#cloud_functions(12458): at android.os.MessageQueue.next(MessageQueue.java:334)
E/MethodChannel#cloud_functions(12458): at android.os.Looper.loop(Looper.java:174)
E/MethodChannel#cloud_functions(12458): at android.app.ActivityThread.main(ActivityThread.java:6939)
E/MethodChannel#cloud_functions(12458): at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#cloud_functions(12458): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
E/MethodChannel#cloud_functions(12458): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:870)
E/flutter (12458): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: Exception: Unable to call function getUserData
E/flutter (12458): #0 HttpsCallable.call (package:cloud_functions/src/https_callable.dart:50:9)
E/flutter (12458): <asynchronous suspension>
E/flutter (12458): #1 _HomePageState._callable (package:firebaselogin/homepage.dart:160:35)
E/flutter (12458): <asynchronous suspension>
E/flutter (12458): #2 _HomePageState.build.<anonymous closure> (package:firebaselogin/homepage.dart:97:23)
E/flutter (12458): #3 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:779:19)
E/flutter (12458): #4 _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:862:36)
E/flutter (12458): #5 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter (12458): #6 TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:504:11)
E/flutter (12458): #7 BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:282:5)
E/flutter (12458): #8 BaseTapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:217:7)
E/flutter (12458): #9 PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:475:9)
E/flutter (12458): #10 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:76:12)
E/flutter (12458): #11 PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:122:9)
E/flutter (12458): #12 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
E/flutter (12458): #13 PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:120:18)
E/flutter (12458): #14 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:106:7)
E/flutter (12458): #15 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
E/flutter (12458): #16 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
E/flutter (12458): #17 GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
E/flutter (12458): #18 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
E/flutter (12458): #19 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
E/flutter (12458): #20 _rootRunUnary (dart:async/zone.dart:1196:13)
E/flutter (12458): #21 _CustomZone.runUnary (dart:async/zone.dart:1085:19)
E/flutter (12458): #22 _CustomZone.runUnaryGuarded (dart:async/zone.dart:987:7)
E/flutter (12458): #23 _invoke1 (dart:ui/hooks.dart:275:10)
E/flutter (12458): #24 _dispatchPointerDataPacket (dart:ui/hooks.dart:184:5)

Answer 1

Callable functions must return a promise that resolves with the data to send to the client. Right now, your function actually isn't returning anything at all. You should probably return the promise returned by get().
exports.getUserData = functions.https.onCall((data) => {
const test = data.text;
return db.collection('users').doc(test).get();
});