code: static List<String> keyValueString(@Nullable Map<?, ?> keyValueMapping) {
      List<String> result = Lists.newArrayList();
      if (keyValueMapping != null && keyValueMapping.size() > 0) {
        for (Map.Entry<?, ?> entry : keyValueMapping.entrySet()) {
          result.add(entry.getKey() + "=" + entry.getValue());
        }
        Joiner joiner = Joiner.on(",");
        return Collections.singletonList(joiner.join(result));
      }
  
      return Collections.emptyList();
    }
docs: Produces a single element list with a key/value pair comma separated string from a {@link Map}.
  
  @return {@code ["key1=value1,key2=value2,..."]} or {@code []} if keyValueMapping=empty/null