Ambiguous method signature on NULL value

The compiler cannot figure out which method to call here in the anonymous window because you are calling with 'null' explicitly vs having a variable type which it can use to figure out what you want. So, for example this code would work just fine:

String test = null;
new myClass(test);

Or, you could do:

new myClass((String)null);

In both cases we are providing the compiler with the information it needs to figure out which method to call.