feat: add error helper method

Author: robert-virkus

lib/src/mime_media_provider.dart

@@ -1,5 +1,6 @@
 import 'package:enough_mail/enough_mail.dart';
 import 'package:enough_media/enough_media.dart';
+import 'package:flutter/foundation.dart';
 
 /// Provides a simple way to generate a media provider from a mime message
 class MimeMediaProviderFactory {
@@ -14,13 +15,26 @@ class MimeMediaProviderFactory {
         name.isNotEmpty) {
       mediaType = MediaType.guessFromFileName(name);
     }
-    if (mediaType.isText) {
-      return TextMediaProvider(
-          name, mediaType.text, mimePart.decodeContentText()!);
-    } else {
-      return MemoryMediaProvider(
-          name, mediaType.text, mimePart.decodeContentBinary()!,
-          description: mimeMessage.decodeSubject());
-    }
+    return mediaType.isText
+        ? TextMediaProvider(
+            name, mediaType.text, mimePart.decodeContentText() ?? '')
+        : MemoryMediaProvider(
+            name,
+            mediaType.text,
+            mimePart.decodeContentBinary() ?? Uint8List(0),
+            description: mimeMessage.decodeSubject(),
+          );
   }
+
+  /// Creates a new [TextMediaProvider] or [MemoryMediaProvider] from
+  /// the given [title] and [text].
+  static MediaProvider fromError({
+    required String title,
+    required String text,
+  }) =>
+      TextMediaProvider(
+        title,
+        MediaType.textPlain.text,
+        text,
+      );
 }