Address invalid embed_json values

app/services/metrics/dashboard/transient_embed_service.rb

@@ -24,6 +24,8 @@ module Metrics
       override :get_raw_dashboard
       def get_raw_dashboard
         JSON.parse(params[:embed_json])
+      rescue JSON::ParserError => e
+        invalid_embed_json!(e.message)
       end
 
       override :sequence
@@ -35,6 +37,10 @@ module Metrics
       def identifiers
         Digest::SHA256.hexdigest(params[:embed_json])
       end
+
+      def invalid_embed_json!(message)
+        raise DashboardProcessingError.new("Parsing error for param :embed_json. #{message}")
+      end
     end
   end
 end

spec/services/metrics/dashboard/transient_embed_service_spec.rb

@@ -67,6 +67,12 @@ describe Metrics::Dashboard::TransientEmbedService, :use_clean_rails_memory_stor
       expect(get_type_for_embed(alt_embed)).to eq('area-chart')
     end
 
+    context 'when embed_json cannot be parsed as json' do
+      let(:embed_json) { '' }
+
+      it_behaves_like 'misconfigured dashboard service response', :unprocessable_entity
+    end
+
     private
 
     def get_embed_json(type = 'line-graph')