src/lic/ppl/world/diff.py [77:101]:
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    def get_node(self, node: RVIdentifier) -> Optional[Variable]:
        """
        Get the node in the diff.

        :params node: the RVIdentifier of the node to be looked up in the diff.
        :returns: the variable of the node in the diff and None if the node
        does not exist.
        """
        if node in self.data_:
            return self.data_[node]
        return None

    def get_node_raise_error(self, node: RVIdentifier) -> Variable:
        """
        Get the node in the diff and raise a ValueError if the node does not
        exists in the diff.

        :params node: the RVIdentifier of node to be looked up in the diff.
        :returns: the variable of the node in the diff and raises an error if
        the node does not exist.
        """
        var = self.get_node(node)
        if var is None:
            raise ValueError(f"Node {node} is missing")
        return var
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src/lic/ppl/world/world_vars.py [60:84]:
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    def get_node(self, node: RVIdentifier) -> Optional[Variable]:
        """
        Get the node in WorldVars.

        :params node: the RVIdentifier of the node to be looked up in WorldVars.
        :returns: the variable of the node in WorldVars and None if the node
        does not exist.
        """
        if node in self.data_:
            return self.data_[node]
        return None

    def get_node_raise_error(self, node: RVIdentifier) -> Variable:
        """
        Get the node in WorldVars and raise a ValueError if the node does not
        exists.

        :params node: the RVIdentifier of node to be looked up in WorldVars.
        :returns: the variable of the node in WorldVars and raises an error if
        the node does not exist.
        """
        var = self.get_node(node)
        if var is None:
            raise ValueError(f"Node {node} is missing")
        return var
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