example:
/fill -8 202 6 -5 202 6 minecraft:unpowered_comparator 0 replace stone
->
Data tag parsing failed: Invalid tag encountered, expected '{' as first char.
But:
/fill -8 202 6 -5 202 6 minecraft:unpowered_repeater 0 replace stone
and
/fill -8 202 6 -5 202 6 minecraft:unpowered_comparator
works.
Fill replace does not work for data holder blocks.