FULL PRODUCT VERSION :
Tested on Java 8, 9 (various versions) and recent EA:

Java(TM) SE Runtime Environment (build 9-ea+109-2016-03-09-181019.javare.4620.nc)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+109-2016-03-09-181019.javare.4620.nc, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Windows 10, 64-bit.

A DESCRIPTION OF THE PROBLEM :
Internal error on toRealPath when path contains a junction.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
mkdir foo
mklink /J bar foo
java -cp . Test bar

The Test.java code is:
import java.io.*;
import java.nio.file.*;

public class Test {
  public static void main(String[] args) throws Exception {
    Path p = Paths.get(args[0]);
    System.out.println("p.toRealPath(): " + p.toRealPath());
  }
}


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Should work.
ACTUAL -
Throws an exception:

Exception in thread "main" java.lang.InternalError: Should not get here
        at sun.nio.fs.WindowsNativeDispatcher.GetFinalPathNameByHandle(Native Method)
        at sun.nio.fs.WindowsLinkSupport.getFinalPath(WindowsLinkSupport.java:77)
        at sun.nio.fs.WindowsLinkSupport.getRealPath(WindowsLinkSupport.java:242)
        at sun.nio.fs.WindowsPath.toRealPath(WindowsPath.java:840)
        at sun.nio.fs.WindowsPath.toRealPath(WindowsPath.java:44)
        at Test.main(Test.java:10)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
Trivial:

public class Test {
  public static void main(String[] args) throws Exception {
    Path p = Paths.get(args[0]);
    System.out.println("p.toRealPath(): " + p.toRealPath());
  }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None known.