Unable to use ChatwootChat-Widget without a ChatwootUser

[konstantinullrich]

Using the ChatwootChat without a ChatwootUser or a ChatwootUser without an email is currently impossible, despite user being nullable.

======== Exception caught by Flutter framework =====================================================
The following _CastError was thrown:
type 'Null' is not a subtype of type 'String' in type cast

When the exception was thrown, this was the stack: 
#0      _$ChatwootContactFromJson (package:chatwoot_sdk/data/local/entity/chatwoot_contact.g.dart:65:26)
#1      new ChatwootContact.fromJson (package:chatwoot_sdk/data/local/entity/chatwoot_contact.dart:46:7)
#2      ChatwootClientAuthServiceImpl.createNewContact (package:chatwoot_sdk/data/remote/service/chatwoot_client_auth_service.dart:40:41)
<asynchronous suspension>
#3      ChatwootClientApiInterceptor.onRequest.<anonymous closure> (package:chatwoot_sdk/data/remote/service/chatwoot_client_api_interceptor.dart:37:19)
<asynchronous suspension>
#4      BasicLock.synchronized (package:synchronized/src/basic_lock.dart:33:16)
<asynchronous suspension>
#5      ChatwootClientApiInterceptor.onRequest (package:chatwoot_sdk/data/remote/service/chatwoot_client_api_interceptor.dart:29:5)
<asynchronous suspension>
I/flutter (18358): #5      ChatwootClientApiInterceptor.onRequest (package:chatwoot_sdk/data/remote/service/chatwoot_client_api_interceptor.dart:29:5)
====================================================================================================

======== Exception caught by Flutter framework =====================================================
The following _CastError was thrown:
type 'Null' is not a subtype of type 'String' in type cast

When the exception was thrown, this was the stack: 
#0      _$ChatwootContactFromJson (package:chatwoot_sdk/data/local/entity/chatwoot_contact.g.dart:65:26)
#1      new ChatwootContact.fromJson (package:chatwoot_sdk/data/local/entity/chatwoot_contact.dart:46:7)
#2      ChatwootClientAuthServiceImpl.createNewContact (package:chatwoot_sdk/data/remote/service/chatwoot_client_auth_service.dart:40:41)
<asynchronous suspension>
#3      ChatwootClientApiInterceptor.onRequest.<anonymous closure> (package:chatwoot_sdk/data/remote/service/chatwoot_client_api_interceptor.dart:37:19)
<asynchronous suspension>
#4      BasicLock.synchronized (package:synchronized/src/basic_lock.dart:33:16)
<asynchronous suspension>
#5      ChatwootClientApiInterceptor.onRequest (package:chatwoot_sdk/data/remote/service/chatwoot_client_api_interceptor.dart:29:5)
<asynchronous suspension>
====================================================================================================