Add support for serializing "empty" Records (and tests)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/ser/BeanSerializerFactory.java

@@ -463,7 +463,12 @@ protected JsonSerializer<Object> constructBeanOrAddOnSerializer(SerializerProvid
             return prov.reportBadTypeDefinition(beanDesc, "Failed to construct BeanSerializer for %s: (%s) %s",
                     beanDesc.getType(), e.getClass().getName(), e.getMessage());
         }
-        if (ser == null) {
+        if (ser == null) { // Means that no properties were found
+            // 21-Aug-2020, tatu: Empty Records should be fine tho
+            if (type.isRecordType()) {
+                return builder.createDummy();
+            }
+
             // 06-Aug-2019, tatu: As per [databind#2390], we need to check for add-ons here,
             //    before considering fallbacks
             ser = (JsonSerializer<Object>) findSerializerByAddonType(config, type, beanDesc, staticTyping);

src/test-jdk14/java/com/fasterxml/jackson/databind/RecordTest.java

@@ -30,6 +30,9 @@ record JsonIgnoreRecord(int id, @JsonIgnore String name) {
     record JsonPropertyRenameRecord(int id, @JsonProperty("rename")String name) {
     }
 
+    record EmptyRecord() {
+    }
+
     private final ObjectMapper MAPPER = newJsonMapper();
 
     /*
@@ -65,16 +68,23 @@ public void testRecordJavaType() {
      */
 
     public void testSerializeSimpleRecord() throws Exception {
-        SimpleRecord record = new SimpleRecord(123, "Bob");
-
-        String json = MAPPER.writeValueAsString(record);
+        String json = MAPPER.writeValueAsString(new SimpleRecord(123, "Bob"));
         final Object EXP = map("id", Integer.valueOf(123), "name", "Bob");
         assertEquals(EXP, MAPPER.readValue(json, Object.class));
     }
 
     public void testDeserializeSimpleRecord() throws Exception {
-        SimpleRecord value = MAPPER.readValue("{\"id\":123,\"name\":\"Bob\"}", SimpleRecord.class);
-        assertEquals(new SimpleRecord(123, "Bob"), value);
+        assertEquals(new SimpleRecord(123, "Bob"),
+                MAPPER.readValue("{\"id\":123,\"name\":\"Bob\"}", SimpleRecord.class));
+    }
+
+    public void testSerializeEmptyRecord() throws Exception {
+        assertEquals("{}", MAPPER.writeValueAsString(new EmptyRecord()));
+    }
+
+    public void testDeserializeEmptyRecord() throws Exception {
+        assertEquals(new EmptyRecord(),
+                MAPPER.readValue("{}", EmptyRecord.class));
     }
 
     public void testSerializeRecordOfRecord() throws Exception {