code: public static HystrixCommandMetrics getInstance(HystrixCommandKey key, HystrixCommandGroupKey commandGroup, HystrixCommandProperties properties) {
          return getInstance(key, commandGroup, null, properties);
      }
docs: Get or create the {@link HystrixCommandMetrics} instance for a given {@link HystrixCommandKey}.
  <p>
  This is thread-safe and ensures only 1 {@link HystrixCommandMetrics} per {@link HystrixCommandKey}.
  
  @param key
  {@link HystrixCommandKey} of {@link HystrixCommand} instance requesting the {@link HystrixCommandMetrics}
  @param commandGroup
  Pass-thru to {@link HystrixCommandMetrics} instance on first time when constructed
  @param properties
  Pass-thru to {@link HystrixCommandMetrics} instance on first time when constructed
  @return {@link HystrixCommandMetrics}