code: function flattenBody (body, bodyStructure) {
    for (const elName in body) {
      if (body[elName].length === 1 && !bodyStructure[elName].alwaysArray) {
        body[elName] = body[elName][0];
      }
    }
  }
docs: /* Flattens body (if there is only one element, make it no-array)