Use fork of function_types which has null safety

pubspec.lock

@@ -432,9 +432,11 @@ packages:
   function_types:
     dependency: "direct main"
     description:
-      name: function_types
-      url: "https://pub.dartlang.org"
-    source: hosted
+      path: "."
+      ref: HEAD
+      resolved-ref: d78adbc6c616c358b358c9a0a7431d22f0794a90
+      url: "https://github.com/GitJournal/function_types.git"
+    source: git
     version: "0.0.2"
   git_bindings:
     dependency: "direct main"

pubspec.yaml

@@ -47,7 +47,8 @@ dependencies:
   flutter_staggered_grid_view: ^0.3.0
   flutter_svg: ^0.21.0-nullsafety.0
   font_awesome_flutter: ^8.7.0
-  function_types: ^0.0.2
+  function_types:
+    git: https://github.com/GitJournal/function_types.git
   google_fonts: ^2.0.0
   http: ^0.13.1
   image_picker: ^0.7.3