@Nullable
    public Ref<PyType> get(@NotNull PyFunction function, @Nullable PyCallSiteExpression callSite, @NotNull TypeEvalContext context) {
      return Optional
        .ofNullable(function.getContainingClass())
        .map(pyClass -> myStringToReturnTypeMap.get(pyClass.getQualifiedName()))
        .map(typeCallback -> typeCallback.getType(callSite, getQualifierType(callSite, context), context))
        .map(Ref::create)
        .orElse(null);
    }
@Nullable
    public Ref<PyType> get(@NotNull PyFunction function, @Nullable PyCallSiteExpression callSite, @NotNull TypeEvalContext context)