Allow null SchemaRegistryClient in AsyncSerde constructor (#2267) (#2304)

Co-authored-by: Robert Yokota <[email protected]>

Author: yinzara

src/Confluent.SchemaRegistry/AsyncSerde.cs

@@ -51,9 +51,11 @@ protected AsyncSerde(ISchemaRegistryClient schemaRegistryClient, SerdeConfig con
 
             if (config == null) { return; }
 
-            IEnumerable<KeyValuePair<string, string>> ruleConfigs = schemaRegistryClient.Config.Concat(config
+            IEnumerable<KeyValuePair<string, string>> ruleConfigs = config
                 .Select(kv => new KeyValuePair<string, string>(
-                    kv.Key.StartsWith("rules.") ? kv.Key.Substring("rules.".Length) : kv.Key, kv.Value)));
+                    kv.Key.StartsWith("rules.") ? kv.Key.Substring("rules.".Length) : kv.Key, kv.Value));
+            if (schemaRegistryClient != null)
+                ruleConfigs = schemaRegistryClient.Config.Concat(ruleConfigs);
 
             foreach (IRuleExecutor executor in this.ruleExecutors.Concat(RuleRegistry.GetRuleExecutors()))
             {

test/Confluent.SchemaRegistry.Serdes.UnitTests/ProtoSerializeDeserialize.cs

@@ -393,5 +393,12 @@ message PersonWithPic {
             Assert.True(pic.SequenceEqual(result.Picture));
         }
 
+        [Fact]
+        public void ProtobufDeserializerWithoutSchemaRegistry()
+        {
+            new ProtobufDeserializer<Person>();
+            Assert.True(true); // if constructor does not throw exception we're ok
+        }
+
     }
 }