Types error with setting deserialize in v6.0.0

Hi there, we override deserialize to use yaml instead; this previously use to work but a change in the typings of conf now means it doesn't compile in typescript.

serialize: yaml.safeDump,
deserialize: yaml.safeLoad,

Error:

Type '(str: string, opts?: LoadOptions | undefined) => string | object | undefined' is not assignable to type 'Deserialize<Record<string, any>>'.
  Type 'string | object | undefined' is not assignable to type 'Record<string, any>'.
    Type 'undefined' is not assignable to type 'Record<string, any>'.ts(2322)