RFR: JDK-8154498: fix to 8154403 results in failure of UserModuleTest.java on all platforms

[Xueming Shen]

Hi,

Please help review the test case only change for JDK-8154498

issue: https://bugs.openjdk.java.net/browse/JDK-8154498
webrev: http://cr.openjdk.java.net/~sherman/8154498/webrev/

A "empty" map need to be passed in as the parameter for 
FileSystems.newFileSystem(),
instead of "null".

Thanks,
Sherman