Depends First of all, did you itemize deductions on your joint 2014 return? If not, then it doesn't matter who claims the refund. It had no benefit in 2014 so it's not taxable in 2015 to either party.
Normally if you filed a joint return in the previous year, the state will report the state refund on your 1099-G and to the IRS under both of your names and social security numbers as though you were still married. Not sure why only your ex was reported. So you could take the chance that the state made a mistake in reporting only your ex-husband's SSN to the IRS, and let him claim the refund.
If you want to stay on the safe side, however, you may just want to split the refund. Either 50/50 or agree on some sort of percentage.