I had something similar happen to me when I moved to TN and applied for my HCP. An old arrest/conviction in California, charges and case were dismissed. I had already purchsed several firearms over the recent years and held a valid, current Illinois Concealed Carry Permit and we all know how difficult it is to get one of those. However, TN still required a disposition of the Cali case. Like you, the record of the case had been destroyed. I, however, had a copy of the adjudication of dismissal (thank goodness) and sent it to Nashville. Still, it didn't satisfy their requirements.
I ended up hiring an attorney in California (in the county that handled the case) for $500 and got the record expunged. Only then did TBI approve my application.
Good luck.