<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_section(self, name):
 """Append `section` to model Arguments: name (str):
 Name of section """


        assert isinstance(name, str)

        # Skip existing sections
        for section in self.sections:
            if section.name == name:
                return section

        item = defaults["common"].copy()
        item["name"] = name

        item["itemType"] = "section"

        item = self.add_item(item)
        self.sections.append(item)

        return item