Operator precedence bug in configureLastModifiedHeader — isOverwritten is never used.
The ! (logical NOT) operator has higher precedence than ===. So !obj.__rerum.isOverwritten === "" evaluates as (!obj.__rerum.isOverwritten) === "", which compares a boolean to a string — this is always false. As a result, the isOverwritten date is never used and the function always falls through to createdAt.