Assert that font is not nil
Assert that font is not nil

hejunbinlan/ASValueTrackingSlider,alskipp/ASValueTrackingSlider,shenyuan000/ASValueTrackingSlider,vantientu1703/ASValueTrackingSlider,vince4/ASValueTrackingSlider,jianyelijun/ASValueTrackingSlider,elegion/ios-pods-ASValueTrackingSlider,puvanarajan/ASValueTrackingSlider,ezescaruli/ASValueTrackingSlider,3squared/ASValueTrackingSlider