FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
>ver

Microsoft Windows [Version 6.1.7601]

EXTRA RELEVANT SYSTEM CONFIGURATION :
Using Cygwin:

$ uname -r
2.0.4(0.287/5/3)

A DESCRIPTION OF THE PROBLEM :
First spotted in this question: http://stackoverflow.com/q/23650709/113632

The behavior of Classloader.getResources() is undefined if passed null, and actually successfully returns an Enumeration. However if you attempt to iterate over the returned object, you get a NullPointerException several layers down into sun.misc. code.

At a minimum, it'd be nice if the ClassLoader documentation could specify what will happen on null arguments. Even better, either Classloader.getResources() should raise an NPE immediately, or the returned Enumeration should be made null-safe if failing-fast isn't possible.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
$ cat ClassLoaderNPE.java
import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;

public class ClassLoaderNPE {
  public static void main(String[] args) throws IOException {
      Enumeration<URL> urls = ClassLoader.getSystemClassLoader().getResources(null);
      System.out.println(urls.hasMoreElements());
  }
}

$ javac ClassLoaderNPE.java

$ java -cp . ClassLoaderNPE
Exception in thread "main" java.lang.NullPointerException
        at sun.misc.MetaIndex.mayContain(Unknown Source)
        at sun.misc.URLClassPath$JarLoader.getResource(Unknown Source)
        at sun.misc.URLClassPath$2.next(Unknown Source)
        at sun.misc.URLClassPath$2.hasMoreElements(Unknown Source)
        at java.lang.ClassLoader$2.hasMoreElements(Unknown Source)
        at sun.misc.CompoundEnumeration.next(Unknown Source)
        at sun.misc.CompoundEnumeration.hasMoreElements(Unknown Source)
        at sun.misc.CompoundEnumeration.next(Unknown Source)
        at sun.misc.CompoundEnumeration.hasMoreElements(Unknown Source)
        at ClassLoaderNPE.main(ClassLoaderNPE.java:8)


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A) NullPointerException or IllegalArgumentException in ClassLoader.getResources()
B) Different Exception with clearer error message from Enumeration.hasMoreElements()
C) Enumeration.hasMoreElements() successfully returns a value
ACTUAL -
Confusing NPE deep in sun.misc.MetaIndex.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.lang.NullPointerException
        at sun.misc.MetaIndex.mayContain(Unknown Source)
        at sun.misc.URLClassPath$JarLoader.getResource(Unknown Source)
        at sun.misc.URLClassPath$2.next(Unknown Source)
        at sun.misc.URLClassPath$2.hasMoreElements(Unknown Source)
        at java.lang.ClassLoader$2.hasMoreElements(Unknown Source)
        at sun.misc.CompoundEnumeration.next(Unknown Source)
        at sun.misc.CompoundEnumeration.hasMoreElements(Unknown Source)
        at sun.misc.CompoundEnumeration.next(Unknown Source)
        at sun.misc.CompoundEnumeration.hasMoreElements(Unknown Source)
        at ClassLoaderNPE.main(ClassLoaderNPE.java:8)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;

public class ClassLoaderNPE {
  public static void main(String[] args) throws IOException {
      Enumeration<URL> urls = ClassLoader.getSystemClassLoader().getResources(null);
      System.out.println(urls.hasMoreElements());
  }
}
---------- END SOURCE ----------