Commercial/Residential Appraisal. comps or cap rate?

[Nicholas Miller]

I own a building that 8,600 sq ft it has two commercial storefronts, a two bay garage area and 6 residential apartments.  Comps for the building are... seemingly impossible to find as the only buildings like it are sold without occupants whereas this building is 80% full and should be 100% full by the end of the year.  

Since comps would be difficult I believe an appraiser would appraise the building based on income.  Is there a standard cap rate in multi-use buildings would fall under for an appraiser?

Am I wrong in making the assumption that an appraiser would not use comps based on occupancy?