code: public String getString(String name, String defaultValue) {
      org.jmxtrans.agent.util.json.JsonValue value = get(name);
      return value != null ? value.asString() : defaultValue;
    }
docs: Returns the <code>String</code> value of the member with the specified name in this object. If
  this object does not contain a member with this name, the given default value is returned. If
  this object contains multiple members with the given name, the last one is picked. If this
  member's value does not represent a JSON string, an exception is thrown.
  
  @param name
  the name of the member whose value is to be returned
  @param defaultValue
  the value to be returned if the requested member is missing
  @return the value of the last member with the specified name, or the given default value if
  this object does not contain a member with that name