NativeImageResourceFileSystem should throw NPE when uri is null.

Author: jovanstevanovic

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/resources/NativeImageResourceFileSystemProvider.java

@@ -140,6 +140,9 @@ public FileSystem newFileSystem(Path path, Map<String, ?> env) {
     public FileSystem getFileSystem(URI uri) {
         try {
             readLock.lock();
+            if (uri == null) {
+                throw new NullPointerException();
+            }
             if (fileSystem == null) {
                 throw new FileSystemNotFoundException("The Native Image Resource File System is not present. " +
                                 "Please create a new file system using the `newFileSystem` operation before attempting any file system operations on resource URIs.");