docs: public static String repeat(String string, String separator, int count) {
  		// 参数验证
  		$.checkNotNull(string);
  		Preconditions.checkArgument(count >= 0, "invalid count: %s", count);
  		String sep = null == separator ? "" : separator;
  
  		StringBuffer sb = new StringBuffer();
  		int forCount = count - 1;
  		for (int i = 0; i < forCount; i++) {
  			sb.append(string).append(sep);
  		}
  		sb.append(string);
  
  		return sb.toString();
  	}