Yes, having gone through this process last year, you would just put 0 for the adjustment if no securities were held in the account in question. 3115 basically just announces to the IRS that the account is going to be MTM from this year forward (you only file it once unless you want to change the accounting method again).
For anyone else who's confused about what the 481(a) adjustment is for traders, it basically tells the IRS, "This is the total net gain/loss of the positions I'm carrying over if I were to sell them at the end of the year before I change the accounting method."
As a trader, I would suggest using software like Tradelog to easily create the necessary accounting forms while just inputting the net totals into the TurboTax software for form 4797.
A lot of the jargon used by accountants and the IRS is just to gatekeep. Like in many disciplines, the abstract vocabulary is used to make you more dependent on "experts in the field" for explanations.
