Some of the API clients (such as Java, C#, and others) will require you to define additional content as part of the class, depending on the best practices for those clients and class definitions. An example of this for the Java API client can be viewed here: How can I extract snippets and highlights with Java API client?
If a set of parameters is getting a result when you query the endpoint in isolation (such as on the dashboard) but you are not getting the same result with your client, you should check that you have definitions for those items to be returned into. As the linked article shows, a property definition for snippetResult in Java, for example, will look like this:
private Object snippetResult;