var target = "Homer";
target.ShouldBeNull();

target
    should be null but was
"Homer"

var target = "Homer";
target.ShouldBeNullOrEmpty();

target ("Homer")
    should be null or empty

var target = "Homer";
target.ShouldBeEmpty();

target
    should be empty but was
"Homer"

string? target = null;
target.ShouldNotBeNull();

target
    should not be null but was

var target = "";
target.ShouldNotBeNullOrEmpty();

target ("")
    should not be null or empty

var target = "";
target.ShouldNotBeNullOrEmpty();

target
    should not be empty but was