fix test on names in likelihood components

to work with literal models

test/pointwise_logdensities.jl

@@ -17,11 +17,11 @@
 
         # Compute the pointwise loglikelihoods.
         lls = pointwise_loglikelihoods(model, vi)
-        @test [:x] ==  unique(DynamicPPL.getsym.(keys(lls)))
         if isempty(lls)
             # One of the models with literal observations, so we'll set this to 0 for subsequent comparisons.
             loglikelihood_true = 0.0
         else
+            @test [:x] ==  unique(DynamicPPL.getsym.(keys(lls)))
             loglikelihood_sum = sum(sum, values(lls))
             @test loglikelihood_sum ≈ loglikelihood_true
         end