Strange Jackson Illegal character ((CTRL-CHAR, code 0)) Exception in Map Reduce Combiner
You can use StringUtils from apache commons to escape the string - https://commons.apache.org/proper/commons-lang/javadocs/api-2.6/src-html/org/apache/commons/lang/StringEscapeUtils.html#line.89
or you can replace selectively the control characters from the string before json marshaling.
you can also refer to this post - Illegal character - CTRL-CHAR