<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_dsl_by_hash(self, node_hash: str) -> Optional[BaseEntity]: """Look up a node by the hash and returns the corresponding PyBEL node tuple."""

        node = self.get_node_by_hash(node_hash)
        if node is not None:
            return node.as_bel()