Fix serialization of Avro null values

Author: marcospassos

avro/src/main/java/com/fasterxml/jackson/dataformat/avro/schema/AvroSchemaHelper.java

@@ -7,6 +7,7 @@
 import java.net.URL;
 import java.util.*;
 
+import org.apache.avro.JsonProperties;
 import org.apache.avro.Schema;
 import org.apache.avro.Schema.Parser;
 import org.apache.avro.reflect.AvroAlias;
@@ -360,17 +361,33 @@ public static String getFullName(Schema schema) {
         }
     }
 
+    public static JsonNode nullNode() {
+        return DEFAULT_VALUE_MAPPER.nullNode();
+    }
+
     /**
      * @since 2.11
      */
     public static JsonNode objectToJsonNode(Object defaultValue) {
+        if (defaultValue == JsonProperties.NULL_VALUE) {
+            return nullNode();
+        }
+
         return DEFAULT_VALUE_MAPPER.convertValue(defaultValue, JsonNode.class);
     }
 
     /**
      * @since 2.11
      */
     public static Object jsonNodeToObject(JsonNode defaultJsonValue) {
+        if (defaultJsonValue == null) {
+            return null;
+        }
+
+        if (defaultJsonValue.isNull()) {
+            return JsonProperties.NULL_VALUE;
+        }
+
         return DEFAULT_VALUE_MAPPER.convertValue(defaultJsonValue, Object.class);
     }
 

avro/src/test/java/com/fasterxml/jackson/dataformat/avro/schema/AvroSchemaHelperTest.java

@@ -0,0 +1,28 @@
+package com.fasterxml.jackson.dataformat.avro.schema;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import static com.fasterxml.jackson.dataformat.avro.schema.AvroSchemaHelper.jsonNodeToObject;
+import static com.fasterxml.jackson.dataformat.avro.schema.AvroSchemaHelper.objectToJsonNode;
+import junit.framework.TestCase;
+import org.apache.avro.JsonProperties;
+
+public class AvroSchemaHelperTest extends TestCase {
+	private static final JsonNodeFactory NODE_FACTORY = new ObjectMapper().getNodeFactory();
+
+	public void testObjectToJsonNode() {
+		assertEquals(NODE_FACTORY.nullNode(), objectToJsonNode(null));
+		assertEquals(NODE_FACTORY.nullNode(), objectToJsonNode(JsonProperties.NULL_VALUE));
+		assertEquals(NODE_FACTORY.booleanNode(true), objectToJsonNode(true));
+		assertEquals(NODE_FACTORY.booleanNode(false), objectToJsonNode(false));
+		assertEquals(NODE_FACTORY.textNode("foo"), objectToJsonNode("foo"));
+	}
+
+	public void testJsonNodeToObject() {
+		assertNull(jsonNodeToObject(null));
+		assertEquals(JsonProperties.NULL_VALUE, jsonNodeToObject(NODE_FACTORY.nullNode()));
+		assertEquals(true, jsonNodeToObject(NODE_FACTORY.booleanNode(true)));
+		assertEquals(false, jsonNodeToObject(NODE_FACTORY.booleanNode(false)));
+		assertEquals("foo", jsonNodeToObject(NODE_FACTORY.textNode("foo")));
+	}
+}