@Nullable
    public ByteIterable get(@NotNull final Transaction txn, @NotNull final ByteIterable first) {
        return this.first.get(txn, first);
    }
@ Nullable public ByteIterable get ( @ NotNull final Transaction txn , @ NotNull final ByteIterable first ) { return this . first . get ( txn , first ) ; }
Search for the first entry in the first database. Use this method for databases configured with no duplicates.

@param txn   enclosing transaction
@param first first key.
@return null if no entry found, otherwise the value.