Why IsNotNullOrEmpty() not exposed for `string`? [closed]

We have created custom Extension method to check IEnumerable is Null Or Empty

public static bool IsNotNullOrEmpty<T>(this IEnumerable<T> listToCheck)
{
   return listToCheck != null && listToCheck.Any();
}

Now Team want to create one more method reverse of above method with name IsNullOrEmpty

Concerns: 1. Should we expose such two function? if Yes -> Why Microsoft and other common library expose only one function Example: String has only IsNullOrEmpty or IsNullOrWhiteSpace not reverse of this function

I have confused about this kind of function. Any suggestion about this and what should we do?