public MemoryLocation getValueAddress() {
            assert (isDefined);
            return valueMemoryLocation;
        }
Returns the address of the value defined at this position.
This points to the first byte of the value data.
Unspecified behavior if the key is not defined.
For efficiency reasons, calls to this method always returns the same MemoryLocation object.
indexr-query-opt/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java