O.Merge drops null types from optional properties of O

[osaton]

🐞 Bug Report

Describe the bug

O.Merge drops null type from optional properties of O since 8.0.5. 8.0.4 works as expected.

Reproduce the bug

type Merged = O.Merge<{
  optionalNull?: string | null | number | boolean;
}, {
  optionalNull2?: string | null | number | boolean;
}>;

Creates type:

type Merged = {
    optionalNull?: string | number | boolean | undefined;
    optionalNull2?: string | number | boolean | null | undefined;
}

Expected behavior (<= 8.0.4)

type Merged = {
    optionalNull?: string | number | boolean | null | undefined;
    optionalNull2?: string | number | boolean | null | undefined;
}

Additional information

• typescript@4.0.3

{
  "compilerOptions": {
    "lib": ["es2017", "DOM"],
    "noImplicitReturns": true,
    "noImplicitAny": true,
    "strict": true,
    "strictNullChecks": true
  }
}

[millsp]

Thank you so much for reporting this. Fix is on the way!