[cross_file] Fix base class nullability (#3629)

Without this, the dummy ("interface") XFile implementation of these properties has different nullability than the others, and the analyzer doesn't match what the runtime actually sees.

Author: stuartmorgan-g

packages/cross_file/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.3.1
+
+* Fix nullability of `XFileBase`'s `path` and `name` to match the
+  implementations to avoid potential analyzer issues.
+
 ## 0.3.0
 
 * Migrated package to null-safety.

packages/cross_file/lib/src/types/base.dart

@@ -31,14 +31,14 @@ abstract class XFileBase {
   /// Accessing the data contained in the picked file by its path
   /// is platform-dependant (and won't work on web), so use the
   /// byte getters in the CrossFile instance instead.
-  String? get path {
+  String get path {
     throw UnimplementedError('.path has not been implemented.');
   }
 
   /// The name of the file as it was selected by the user in their device.
   ///
   /// Use only for cosmetic reasons, do not try to use this as a path.
-  String? get name {
+  String get name {
     throw UnimplementedError('.name has not been implemented.');
   }
 

packages/cross_file/pubspec.yaml

@@ -1,7 +1,7 @@
 name: cross_file
 description: An abstraction to allow working with files across multiple platforms.
 homepage: https://github.com/flutter/plugins/tree/master/packages/cross_file
-version: 0.3.0
+version: 0.3.1
 
 dependencies:
   flutter: