code: public T getService(ServiceReference<T> serviceReference) {
  
          if (serviceReference != null) {
              ComponentContext ctx = contextRef.get();
              if (ctx != null) {
                  ConcurrentServiceReferenceElement<T> element;
                  synchronized (elementMap) {
                      element = elementMap.get(serviceReference);
                  }
                  if (element != null) {
                      return element.getService(ctx);
                  }
              }
          }
          return null;
      }
docs: Find the provided reference in the set, and return the corresponding service.
  Subject to the same restrictions/behavior as getServices.
  
  @param serviceReference Service reference to find in the set
  @return service associated with service reference, or null if the service could not be located.