code: public String getMessage(Throwable exception) {
  		String message;
  		if (getExceptionToMessage() != null) {
  			message = getExceptionToMessage().get(exception.getClass());
  			if (StringUtils.hasText(message)) {
  				return message;
  			}
  
  			// map entry with a null value
  			if (getExceptionToMessage().containsKey(exception.getClass())) {
  				return exception.getMessage();
  			}
  		}
  
  		if (isSendExceptionMessage()) {
  			return exception.getMessage();
  		}
  		return getDefaultExceptionMessage();
  
  	}
docs: Returns an error message for the supplied exception and based on this
  configuration.
  
  @see #setDefaultExceptionMessage(String)
  @see #setSendExceptionMessage(boolean)
  @see #setExceptionToMessage(Map)
  
  @param exception the thrown exception
  @return exception message