Address two review comments

source/heating_model/shear_heating.cc

@@ -88,6 +88,7 @@ namespace aspect
                 }
 
               const MaterialModel::ElasticAdditionalOutputs<dim> *elastic_out = material_model_outputs.template get_additional_output<MaterialModel::ElasticAdditionalOutputs<dim>>();
+              AssertThrow(elastic_out != nullptr, ExcMessage("ElasticAdditionalOutputs are requested, but have not been computed."));
 
               const double shear_modulus = elastic_out->elastic_shear_moduli[q];
 

source/material_model/visco_plastic.cc

@@ -309,9 +309,6 @@ namespace aspect
 
       if (this->get_parameters().enable_elasticity)
         {
-          // TODO check that in.requests_property(MaterialProperties::viscosity) is true,
-          // because we need the viscosities to fill the outputs below
-
           // Fill the force outputs with the body force term for the RHS.
           rheology->elastic_rheology.fill_elastic_force_outputs(in, average_elastic_shear_moduli, out);
           // Fill the reaction terms that account for the rotation of the stresses.