Check engine light on but no code. 1997 Nissan maxima

have seen this many times. i own a transmission shop. a simple clearing of codes turns light off, think is glitch in computer. seems no numbered codes then does not affect running of engine. just simply clear anyway you can buy a cheap code reader/ clearing tool rather cheaply.

thanks, have cleared comp 3 times with obd11, once with battery disconnect, will try switch on computer.