Missed source compatibility problem with ambiguous overloads.

[lbergelson]

When adding additional overloads that have the same number of parameters to an existing method, it causes a potential source compatibility issue due to the type inference of null.

ex:
Existing method

public void doThing(File file){...}

Adding the following overload will cause compilation errors in sites that make a call with a null parameter.

public void doThing(Path path){...}