@Nullable
      @Override
      public String apply(@Nullable String s) {
        if ((m == null) || (!m.containsKey(s))){
          return s;
        }
        return m.get(s);
      }
Utility function to use in conjunction with .withDbNameMapping / .withTableNameMapping,
if we desire usage of a Map<String,String> instead of implementing a Function<String,String>
hcatalog/webhcat/java-client/src/main/java/org/apache/hive/hcatalog/api/repl/ReplicationUtils.java