FIX NoSuchMethodError: java.nio.MappedByteBuffer.duplicate (#453)

Co-authored-by: Maxim Thomas <maxim.thomas@gmail.com>

opendj-server-legacy/src/main/java/org/opends/server/backends/pluggable/OnDiskMergeImporter.java

@@ -1510,7 +1510,7 @@ public MeteredCursor<ByteString, ByteString> flip()
             mmapPosition = region.offset;
             mmap = channel.map(MapMode.READ_ONLY, mmapPosition, Math.min(size.get() - mmapPosition, Integer.MAX_VALUE));
           }
-          final ByteBuffer regionBuffer = mmap.duplicate();
+          final ByteBuffer regionBuffer = ((ByteBuffer)mmap).duplicate();
           final int relativeRegionOffset = (int) (region.offset - mmapPosition);
           regionBuffer.position(relativeRegionOffset).limit(regionBuffer.position() + region.size);
           cursors.add(new FileRegion.Cursor(name, regionBuffer.slice()));