code: @Override
      public Object map(Object input) {
          Number n = (Number) input;
          if (inputSchema.getMetaData(columnNumber).isValid(new IntWritable(n.intValue()))) {
              return input;
          } else {
              return value;
          }
      }
docs: Transform an object
  in to another object
  
  @param input the record to transform
  @return the transformed writable