Warn in check_model if model is empty

Author: penelopeysm

HISTORY.md

@@ -4,6 +4,8 @@
 
 `varinfo[:]` now returns an empty vector if `varinfo::DynamicPPL.NTVarInfo` is empty, rather than erroring.
 
+In its place, `check_model` now issues a warning if the model is empty.
+
 ## 0.36.4
 
 Added compatibility with DifferentiationInterface.jl 0.7, and also with JET.jl 0.10.

src/debug_utils.jl

@@ -338,6 +338,11 @@ function conditioned_varnames(context)
 end
 
 function check_varnames_seen(varnames_seen::AbstractDict{VarName,Int})
+    if isempty(varnames_seen)
+        @warn "The model does not contain any parameters."
+        return true
+    end
+
     issuccess = true
     for (varname, count) in varnames_seen
         if count == 0