I have the following Z80 asm code (from pokemon legacy crystal)

CheckOnWater::
    ld a, [wPlayerStandingTile]
    call GetTileCollision
    sub WATER_TILE
    ret z
    and a
    ret

i was wondering what the point is of

ret z
and a
ret

as i understand, sub WATER_TITLE sets the z flag, it feels redundant to conditionally return, then and a just to set the z flag again and then to return.

can’t i replace the whole three lines by just ret?

what am i missing?