def METHOD_NAME(self, domain_name: str) -> Optional[str]:
    domain_metadata = {
        urn: metadata
        for urn, metadata in self.entity_graph.items()
        if urn.startswith("urn:li:domain:")
    }
    domain_properties_metadata = {
        urn: metadata["domainProperties"].name
        for urn, metadata in domain_metadata.items()
        if "domainProperties" in metadata
        and isinstance(metadata["domainProperties"], DomainPropertiesClass)
    }
    urn_match = [
        urn
        for urn, name in domain_properties_metadata.items()
        if name == domain_name
    ]
    if urn_match:
        return urn_match[0]
    else:
        return None