FULL PRODUCT VERSION :
java version "1.8.0_60"
Java(TM) SE Runtime Environment (build 1.8.0_60-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Mac OS X 10.11

A DESCRIPTION OF THE PROBLEM :
ZipPath does not produce a correct "empty path" when relativizing a path against a equal one.



STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
        try (FileSystem fileSystem = FileSystems.newFileSystem(jarFile, Collections.emptyMap())) {
            Path root = fileSystem.getPath("/");
            Path root2 = fileSystem.getPath("/");
            System.out.println(root.relativize(root2).getNameCount());
        }


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
It should print "1" on console. As the definition of en empty path is: "A Path is considered to be an empty path if it consists solely of one name element that is empty."
ACTUAL -
Prints "0" on console. This means that "this path only represents a root component" (and is therefore absolute).

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.File;
import java.io.IOException;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.util.Collections;

class ZipPathBug {
    public static void main(String[] args) throws IOException {
        URI jarFile = URI.create("jar:" + new File("test.zip").getAbsoluteFile().toURI().toString());
        try (FileSystem fileSystem = FileSystems.newFileSystem(jarFile, Collections.emptyMap())) {
            Path path = fileSystem.getPath("/foo");
            Path path2 = fileSystem.getPath("/foo");
            System.out.println(path.relativize(path2).getNameCount());
        }
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
As getNameCount() is "0" we can check the relative path and use a workaround specific to this case.