`NonNullable<unknown>` => `{}`

[salisbury-espinosa]

Describe the bug

Version: 27.0.2

To Reproduce

source file test.ts:

type TestType = unknown;

analysis file:

import { Project } from 'ts-morph';

const project = new Project({
  tsConfigFilePath: '../tsconfig.json',
});
const sourceFile = project.getSourceFileOrThrow('./test.ts');

const TestType = sourceFile.getTypeAliasOrThrow('TestType').getType();

console.log(
  `TestType.getText(): "${TestType.getText()}", TestType.isUnknown(): ${TestType.isUnknown()}`,
);
console.log(
  `TestType.getNonNullableType().getText(): "${TestType.getNonNullableType().getText()}", TestType.getNonNullableType().isUnknown(): ${TestType.getNonNullableType().isUnknown()}`,
);

Current behavior

TestType.getText(): "unknown", TestType.isUnknown(): true
TestType.getNonNullableType().getText(): "{}", TestType.getNonNullableType().isUnknown(): false

Expected behavior

TestType.getText(): "unknown", TestType.isUnknown(): true
TestType.getNonNullableType().getText(): "unknown", TestType.getNonNullableType().isUnknown(): true