Will an hourly T-Log backup in a Maintenance plan write a file if there are no changes to a DB?
Review the backupset and related tables in msdb as the source for if a successful backup was taken.  If you see gaps in when a scheduled backup was to have occurred, your job either failed or never ran.

Every backup command generates an internal checkpoint, which in turn, moves the log sequence number (lsn).  Review the first_lsn and last_lsn pattern with every log backup in the backupset table.  Likewise, a file will always be generated if your job backs up to a time-stamped filename (default behavior of maintenance plans).  You can verify this behavior by manually/interactively running a log backup command multiple times on a database without an transactions between runs.