Parses <Case>

        @param node: Node containing the <Case> element
        @type node: xml.etree.Element

        @raise ParseError: When no condition or value is specified

def parse_case(self, node):
        """
        Parses <Case>

        @param node: Node containing the <Case> element
        @type node: xml.etree.Element

        @raise ParseError: When no condition or value is specified
        """
        
        try:
            condition = node.lattrib['condition']
        except:
            condition = None
            
        try:
            value = node.lattrib['value']
        except:
            self.raise_error('<Case> must specify a value')

        self.current_conditional_derived_variable.add_case(Case(condition, value))