chore: cleanup MockTransport, moving proper json handling to SentryRe…

…quest

dart/lib/src/protocol/sentry_request.dart

@@ -89,10 +89,10 @@ class SentryRequest {
       queryString: json['query_string'],
       cookies: json['cookies'],
       data: json['data'],
-      headers: json['headers'],
-      env: json['env'],
+      headers: json.containsKey('headers') ? Map.from(json['headers']) : null,
+      env: json.containsKey('env') ? Map.from(json['env']) : null,
       // ignore: deprecated_member_use_from_same_package
-      other: json['other'],
+      other: json.containsKey('other') ? Map.from(json['other']) : null,
       fragment: json['fragment'],
     );
   }

dart/test/mocks/mock_transport.dart

@@ -43,33 +43,7 @@ class MockTransport implements Transport {
 
     final envelopeItem = utf8.decode(envelopeItemData);
     final envelopeItemJson = jsonDecode(envelopeItem.split('\n').last);
-    final envelopeMap = envelopeItemJson as Map<String, dynamic>;
-    final requestJson = envelopeMap['request'] as Map<String, dynamic>?;
-
-    // TODO the following code should really be part of fromJson() that handle those keys.
-    // JSON being Map<String, dynamic> is nothing out of ordinary.
-    // See [SentryResponse.fromJson()] as an example.
-
-    // '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, String>'
-    final headersMap = requestJson?['headers'] as Map<String, dynamic>?;
-    final newHeadersMap = <String, String>{};
-    if (headersMap != null) {
-      for (final entry in headersMap.entries) {
-        newHeadersMap[entry.key] = entry.value as String;
-      }
-      envelopeMap['request']['headers'] = newHeadersMap;
-    }
-
-    final otherMap = requestJson?['other'] as Map<String, dynamic>?;
-    final newOtherMap = <String, String>{};
-    if (otherMap != null) {
-      for (final entry in otherMap.entries) {
-        newOtherMap[entry.key] = entry.value as String;
-      }
-      envelopeMap['request']['other'] = newOtherMap;
-    }
-
-    return SentryEvent.fromJson(envelopeMap);
+    return SentryEvent.fromJson(envelopeItemJson);
   }
 
   void reset() {