MutationFunction TypeScript type incorrect in react-components

[Mike-Gibson]

The type MutationFunction used in react-components returns a Promise<void | MutationFetchResult<TData>> which makes it hard to use the result without first checking the result is defined.

This was discussed in #2095 and a fix was made for react-hooks in #3334 but the issue still remains in react-components.

As far as I'm aware, it would make sense that the mutation function does not return void in both react-hooks and react-components.

The type is defined here:

react-apollo/packages/common/src/types/types.ts

Lines 140 to 145 in 3c961c3

	export declare type MutationFunction<
	TData = any,
	TVariables = OperationVariables
	> = (
	options?: MutationFunctionOptions<TData, TVariables>
	) => Promise<void | MutationFetchResult<TData>>;

This occurs in react-apollo 3.0.1.

[rerissondaniel]

+1