code: public static ValueFilter createValueFilterOfTag(String operation, String tagKey) {
          checkArgument(TAG_SUPPORTED_OPERATION.contains(operation), "Value of tag key only support operations in "
                  + TAG_SUPPORTED_OPERATION.toString());
          ValueFilter valueFilter = new ValueFilter(operation, tagKey);
          return valueFilter;
      }
docs: Create value filter for comparing with the value of tag key.
  
  @param operation Operation for comparing which support =, !=, &gt;, &lt;, &gt;= and &lt;=.
  @param tagKey Value of tag key for comparing with.
  @return ValueFilter