type GraphQLRequestParams<
  Data = any,
  Variables extends AnyVariables = AnyVariables,
> =
  | ({
      query: string | Data;
    } & (Variables extends void
      ? {
          variables?: Variables;
        }
      : Variables extends {
            [P in keyof Variables]: Exclude<Variables[P], null | void>;
          }
        ? Variables extends {
            [P in keyof Variables]: never;
          }
          ? {
              variables?: Variables;
            }
          : {
              variables: Variables;
            }
        : {
            variables?: Variables;
          }))
  | {
      query: string | Data;
      variables: Variables;
    };

export type GraphQLRequestParams<
  Data = any,
  Variables extends AnyVariables = AnyVariables,
> =
  | ({
      query: DocumentInput<Data, Variables>;
    } & (Variables extends void
      ? {
          variables?: Variables;
        }
      : Variables extends {
            [P in keyof Variables]: undefined extends Variables[P]
              ? unknown
              : null extends Variables[P]
                ? unknown
                : void extends Variables[P]
                  ? unknown
                  : never;
          }
        ? {
            variables?: Variables;
          }
        : {
            variables: Variables;
          }))
  | {
      query: DocumentInput<Data, Variables>;
      variables: Variables;
    };

const foo1: GraphQLRequestParams<{a: string; b: number | null}> = {}; // No error, although field `a` is required and non-nullish
const foo2: FixGraphQLRequestParams<{a: string; b: number | null}> = {}; // Error, as expected
const foo3: FixGraphQLRequestParams<{a?: string; b: number | null; c: boolean | undefined; d: string | void}> = {}; // No error -- all fields optional or nullish