Raise an exception instead of attempting to write to an empty topic name

ext/hermann/hermann_lib.c

@@ -487,8 +487,10 @@ static VALUE producer_push_single(VALUE self, VALUE message) {
 
 	Data_Get_Struct(self, HermannInstanceConfig, producerConfig);
 
-	if (producerConfig->topic==NULL) {
-		fprintf(stderr, "Topic is null!");
+	if ((NULL == producerConfig->topic) ||
+		(0 == strlen(producerConfig->topic))) {
+		fprintf(stderr, "Topic is null!\n");
+		rb_raise(rb_eRuntimeError, "Topic cannot be empty");
 		return self;
 	}
 

spec/producer_spec.rb

@@ -7,17 +7,26 @@ describe Hermann::Producer do
   let(:topic) { 'rspec' }
   let(:brokers) { 'localhost:1337' }
 
-  context 'with a bad broker configuration' do
-    let(:brokers) { '' }
-
-    it 'should raise an exception' do
-      expect {
-        producer.push('anything')
-      }.to raise_error(RuntimeError)
-    end
-  end
 
   describe '#push' do
+    context 'error conditions' do
+      shared_examples 'an error condition' do
+        it 'should raise an exception' do
+          expect { producer.push('rspec') }.to raise_error(RuntimeError)
+        end
+      end
+
+      context 'with a bad broker configuration' do
+        let(:brokers) { '' }
+        it_behaves_like 'an error condition'
+      end
+
+      context 'with a bad topic' do
+        let(:topic) { '' }
+        it_behaves_like 'an error condition'
+      end
+    end
+
     subject(:result) { producer.push(value) }
 
     context 'with a single value' do