getExtensionValue() return type is incorrect

[sachin-sunny-rad]

export function getExtensionValue(resource: any, ...urls: string[]): string | undefined 

getExtensionValue() says it will return string | undefined but it actually returns other types aswell:

bot.extension = [
      {
        url: 'url',
        valueBoolean: false,
      },
    ];
const val = getExtensionValue(bot, ...); <- returns boolean

bot.extension = [
      {
        url: 'url',
        valueString: "test",
      },
 ];
const val = getExtensionValue(bot, ...); <- returns string