fix return nothing

src/inputs_from_gene_atlas.jl

@@ -311,6 +311,7 @@ function read_and_validate_estimands(estimands_prefix)
         TargetedEstimation.read_estimands_config(f).estimands for f ∈ files_matching_prefix(estimands_prefix)
     )
     check_only_one_set_of_confounders_per_treatment(estimands)
+    return estimands
 end
 
 """