In the event that there is a problem getting a resource, `URLClassLoader.getResource()` and `findResource()` now return `null` instead of throwing an undocumented `IllegalArgumentException`. The same is true of `Enumeration`s obtained from `URLClassLoader.getResources()` and `URLClassLoader.findResources()`.

This behavior conforms with the long-standing specification. The situation would typically occur on Windows, due to the use of a Windows-style path (`"c:/windows"`).