Using only `GodanConjugationMap` cannot correctly infer some conjugated forms of 「行く」「ある」

[huyi1985]

type GodanConjugationMap = {
  く: {
    ます形: "き";
    て形: "いて";
    ...
  };
  ...
  る: {
    ...
    ない形: "ら";
    ...
  };
};

// Helper utility types for conjugation
type GetGodanConjugation<
  E extends GodanVerb["ending"],
  F extends ConjugationForm
> = F extends keyof GodanConjugationMap[E]
  ? StringLiteral<GodanConjugationMap[E][F]>
  : never;

type 行く = GodanVerb & { stem: "行"; ending: "く" };
type ある = GodanVerb & { stem: "あ"; ending: "る" };

type 行くて形 = ConjugateVerb<行く, "て形">;
type あるない形 = ConjugateVerb<ある, "ない形">;

const wrongIku: 行くて形 = "行いて"
const wrongAru: あるない形 = "あら"

const verifyIku: 行くて形 = "行って" // Type '"行って"' is not assignable to type '"行いて"'.
const verifyAru: あるない形 = ""    // ない。Type '""' is not assignable to type '"あら"'.