V getValidValue() {
            Object v = value;
            if (v == sentinel() || v == BASE_HEADER)
                return null;
            @SuppressWarnings("unchecked") V vv = (V)v;
            return vv;
        }
V getValidValue ( ) { Object v = value ; if ( v == sentinel ( ) || v == BASE_HEADER ) return null ; @ SuppressWarnings ( "unchecked" ) V vv = ( V ) v ; return vv ; }
Returns value if this node contains a valid key-value pair,
else null.
@return this node's value if it isn't a marker or header or
is deleted, else null