RFR 8043252: Debug of access control is obfuscated - NullPointerException in ProtectionDomain

[Jamil Nimeh]

Hello all,

This fixes an issue in ProtectionDomain, where Permission classes that 
take a loose interpretation of the getActions() method and return null 
cause an NPE to be thrown when a ProtectionDomain's toString method is 
called (during debugging for instance).

Bug: https://bugs.openjdk.java.net/browse/JDK-8043252
Webrev: http://cr.openjdk.java.net/~jnimeh/reviews/8043252/webrev.01/

Thanks,
--Jamil