What do I enter in box 15 if the state where I worked is not listed

Several  states do not have a state income tax.  So these states will not show up in certain drop down lists.   Leave boxes 15, 16, and 17 blank when you enter a W-2 for these states.

Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington and Wyoming

Is it a state with no income tax?   Are there any amounts in the boxes 16-20?   If not, leave it blank.