move email class to its own file; make Email type non-null

+## NEXT
+Improvements:
+* The `type` of an `Email` is no longer null.
+
 ## 3.5.0
 New Features:
 * Added the option to switch between bundled and unbundled MLKit for Android. (thanks @woolfred !)

@@ -14,4 +14,5 @@ export 'src/mobile_scanner_controller.dart';
 export 'src/mobile_scanner_exception.dart';
 export 'src/objects/barcode.dart';
 export 'src/objects/barcode_capture.dart';
+export 'src/objects/email.dart';
 export 'src/objects/mobile_scanner_arguments.dart';

@@ -5,9 +5,9 @@ import 'package:mobile_scanner/src/barcode_utility.dart';
 import 'package:mobile_scanner/src/enums/address_type.dart';
 import 'package:mobile_scanner/src/enums/barcode_format.dart';
 import 'package:mobile_scanner/src/enums/barcode_type.dart';
-import 'package:mobile_scanner/src/enums/email_type.dart';
 import 'package:mobile_scanner/src/enums/encryption_type.dart';
 import 'package:mobile_scanner/src/enums/phone_type.dart';
+import 'package:mobile_scanner/src/objects/email.dart';
 
 /// Represents a single recognized barcode and its value.
 class Barcode {
@@ -383,37 +383,6 @@ class DriverLicense {
         middleName = data['middleName'] as String?;
 }
 
-/// An email message from a 'MAILTO:' or similar QRCode type.
-class Email {
-  /// Gets email's address.
-  ///
-  /// Returns null if not available.
-  final String? address;
-
-  /// Gets email's body.
-  ///
-  /// Returns null if not available.
-  final String? body;
-
-  /// Gets email's subject.
-  ///
-  /// Returns null if not available.
-  final String? subject;
-
-  /// Gets type of the email.
-  ///
-  /// See also [EmailType].
-  /// Returns null if not available.
-  final EmailType? type;
-
-  /// Create a [Email] from native data.
-  Email.fromNative(Map data)
-      : address = data['address'] as String?,
-        body = data['body'] as String?,
-        subject = data['subject'] as String?,
-        type = EmailType.values[data['type'] as int];
-}
-
 /// GPS coordinates from a 'GEO:' or similar QRCode type.
 class GeoPoint {
   /// Gets the latitude.

+import 'package:mobile_scanner/src/enums/email_type.dart';
+
+/// An email message from a 'MAILTO:' or similar QRCode type.
+class Email {
+  /// Construct a new [Email] instance.
+  const Email({
+    this.address,
+    this.body,
+    this.subject,
+    this.type = EmailType.unknown,
+  });
+
+  /// Construct an [Email] from the given [data].
+  factory Email.fromNative(Map<Object?, Object?> data) {
+    return Email(
+      address: data['address'] as String?,
+      body: data['body'] as String?,
+      subject: data['subject'] as String?,
+      type: EmailType.fromRawValue(data['type'] as int? ?? 0),
+    );
+  }
+
+  /// The email address.
+  final String? address;
+
+  /// The body of the email.
+  final String? body;
+
+  /// The subject of the email.
+  final String? subject;
+
+  /// The type of the email.
+  final EmailType type;
+}