FetchtResult for mutation

Holla!

.mutate() method of apollo-angular uses FetchResult<T> for the return type, which internally uses ExecutionResult<T> from graphql module itself. The data property in ExecutionResult defined as optional and nullable. This brings problems because TS always complain that data might be null even when your mutation result is neve nullable (we use types generated from the schema). So you have to fight with nullability and of course, it's confusing because the schema result is non-nullable.

In contradiction query method defines data as data<T>, so we don't have this problem for queries.

What would be a solution to this?

Start by comparing the .mutate() and query method return types, especially their use of FetchResult<T>, ExecutionResult<T>, and data<T>. Determine how the mutation result can preserve the schema's non-nullability without producing TypeScript nullability errors, then verify the resulting mutation typing against the query behavior.