code: public static String[] allLowerCase(String... strings){
  		String[] tmp = new String[strings.length];
  		for(int idx=0;idx<strings.length;idx++){
  			if(strings[idx] != null){
  				tmp[idx] = strings[idx].toLowerCase();
  			}
  		}
  		return tmp;
  	}
docs: Make all elements of a String array lower case.
  @param strings string array, may contain null item but can't be null
  @return array containing all provided elements lower case