Can I do an IF Statement in Access with nothing for false expression

I am trying to add an if statement to my Access query where if the month length is equal to 0 it makes the total volume equal to the annualized volume. Below is what I've tried. It keeps asking me to give the term length however so I'm not sure what's wrong.

IIf([TERM_LENGTH]=0,[ProcMWh]=[AMWh])

IIf([TERM_LENGTH]="0",[ProcMWh]=[AMWh], [ProcMWh])

IIf([TERM_LENGTH]="0",[ProcMWh]=[AMWh], "")