code: public Set<ServerSentEventConnection> getConnections(String uri) {
          Objects.requireNonNull(uri, Required.URI.toString());
  
          final Set<ServerSentEventConnection> uriConnections = this.cache.get(Default.SSE_CACHE_PREFIX.toString() + uri);
  
          return (uriConnections == null) ? new HashSet<>() : uriConnections;
      }
docs: Retrieves all connection resources under a given URL
  
  @param uri The URI resource for the connections
  
  @return A Set of connections for the URI resource