<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def check_if_modified_since(self, dt, etag=None):
 """Validate If-Modified-Since with current request conditions."""

        dt = dt.replace(microsecond=0)
        if request.if_modified_since and dt <= request.if_modified_since:
            raise SameContentException(etag, last_modified=dt)