'Widget' is not a subtype of 'Widget' in type cast

I'm getting the following error during the testing of my frontend app.

>'Widget' is not a subtype of type 'Widget'

Here is the detailed trace shown in the console :

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following _TypeError was thrown building StreamBuilder<User>(dirty, state:
_StreamBuilderBaseState<User, AsyncSnapshot<User>>#aebd2):
type '({required BuildContext context, required Post post, required String postIdentifier, required
KNPostDisplayContext displayContext, required (Post) => void onPostDeleted}) => Widget' is not a
subtype of type '({BuildContext context, KNPostDisplayContext displayContext, (Post) => void
onPostDeleted, Post post, String postIdentifier}) => Widget' in type cast

<!-- end snippet -->

Here the Widget code :

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-html -->

  Widget _buildVisibleProfileContent() {
    return Column(
      mainAxisSize: MainAxisSize.max,
      children: [
        Expanded(
          child: KNPostsStream(
              streamIdentifier: 'profile_${widget.user.username}',
              displayContext: _postsDisplayContext,
              prependedItems: _buildProfileContentDetails(),
              controller: _obPostsStreamController,
              postBuilder: _buildPostsStreamPost as KNPostsStreamPostBuilder,
              secondaryRefresher: _refreshUser,
              refresher: _refreshPosts,
              onScrollLoader: _loadMorePosts,
              onPostsRefreshed: _onPostsRefreshed,
              statusIndicatorBuilder: _buildPostsStreamStatusIndicator),
        ),
      ],
    );
  }

<!-- end snippet -->

On debugging, this is the line that is the issue :

> postBuilder: _buildPostsStreamPost as KNPostsStreamPostBuilder,

I upgraded flutter to the latest version : 3.10.1. My pubspec.yaml shows the following:

environment:
sdk: ">=2.12.0 <3.0.0"

I read other answers. Null safety is the reason why there is an issue but can't figure what needs to be done(maybe my lack of flutter knowledge). Earlier flutter versions didn't throw the error.

Help appreciated.

EDIT : upon request by rohan, I am uploading the post_streams.dart

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-html -->

final KNPostsStreamPostBuilder? postBuilder;
 
 
List<Widget> _buildStreamPosts() {
  KNPostsStreamPostBuilder postBuilder =
      widget.postBuilder ?? _defaultStreamPostBuilder;
	 

typedef KNPostsStreamPostBuilder = Widget Function(
    {BuildContext context,
    Post post,
    KNPostDisplayContext displayContext,
    String postIdentifier,
    ValueChanged<Post> onPostDeleted});	 

<!-- end snippet -->

All of the parameters of KNPostsStreamPostBuilder are optional. However, the parameters of _buildPostsStreamPost are required. Therefore, _buildPostsStreamPost cannot be an implementation of KNPostsStreamPostBuilder.

If you control KNPostsStreamPostBuilder, simply make its parameters required.

typedef KNPostsStreamPostBuilder = Widget Function(
    {required BuildContext context,
    required Post post,
    required KNPostDisplayContext displayContext,
    required String postIdentifier,
    required ValueChanged<Post> onPostDeleted});  

In the original app, this function is only called with all five parameters supplied, so this won't break any usages. You can also remove the explicit cast here and the null checks in the other two implementations.