public InternalTopologyBuilder lookupBuilderForNamedTopology(final String topologyName) {
        if (topologyName == null) {
            return builders.get(UNNAMED_TOPOLOGY);
        } else {
            return builders.get(topologyName);
        }
    }
@return the InternalTopologyBuilder for the NamedTopology with the given {@code topologyName}
        or the builder for a regular Topology if {@code topologyName} is {@code null},
        else returns {@code null} if {@code topologyName} is non-null but no such NamedTopology exists
streams/src/main/java/org/apache/kafka/streams/processor/internals/TopologyMetadata.java