Resolving the Null is not subtype of Map String, dynamic Exception in Flutter JSON Parsing

Learn how to fix the common Flutter error `Null is not subtype of Map String, dynamic ` when working with JSON data. This guide provides clear solutions and examples for effective JSON handling in Dart.
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Fixing the Null is not subtype of Map<String, dynamic> Exception in Flutter

When working on a Flutter project, you might encounter various exceptions, one of the most common being the Null is not subtype of Map<String, dynamic> error. This issue typically arises during the process of converting JSON data into Dart objects, especially if there's an inconsistency between the expected structure of your JSON and your Dart model classes. In this guide, we will explore a specific instance of this error and provide you with a comprehensive solution.

Understanding the Problem

Imagine you're developing a YouTube project that pulls data from a JSON API for video searches. Your JSON response contains nested objects, requiring you to create model classes for proper data representation. Here's a brief look at a sample JSON response:

[[See Video to Reveal this Text or Code Snippet]]

In this case, you are trying to convert the pageInfo object into a Dart class called PageInfoData. However, despite your best efforts, you encounter an exception:
Null is not subtype of Map<String, dynamic>.

Analyzing the Code

Let’s break down the key components of your Dart model classes:

PageInfoData Class:
This class is responsible for converting the pageInfo part of the JSON.

[[See Video to Reveal this Text or Code Snippet]]

YouTubeSearchModel Class:
This parent class converts the entire JSON response from the API.

[[See Video to Reveal this Text or Code Snippet]]

In reviewing your code, it appears there are crucial typos that lead to the error:

The Solution

Step-by-Step Fixes

Fix Typos in PageInfoData:

[[See Video to Reveal this Text or Code Snippet]]

Correct the Key in YouTubeSearchModel:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By making the necessary corrections to your model classes as outlined above, you should be able to eliminate the Null is not subtype of Map<String, dynamic> exception when parsing JSON data in your Flutter application. Remember, when working with JSON, it’s essential to ensure that the structure in your Dart code matches precisely with the JSON you are handling. Happy coding!