docs: protected String getOverwriteValue(String fieldname) {
  		ActionContext ctx = ServletActionContext.getContext();
  		ValueStack stack = ctx.getValueStack();
  		Map<Object ,Object> overrideMap = stack.getExprOverrides();
  
  		// If convertion error has not, do nothing.
  		if ( overrideMap == null || overrideMap.isEmpty()) {
  			return null;
  		}
  
  		if (! overrideMap.containsKey(fieldname)) {
  			return null;
  		}
  
  		String convertionValue = (String)overrideMap.get(fieldname);
  
  		// Struts2-Conponent is wrapped String quote, which erase for output value.
  		String altString =  StringEscapeUtils.unescapeJava(convertionValue);
  		altString = altString.substring(1, altString.length() -1);
  
  		return altString;
  	}