Serialize Annotation object with all required fields even empty (#110)

* Serialize Annotation object with all required fields even empty

Having JsonInclude:NON_EMPTY removes empty fields (e.g., "")
When the required fields are removed, API calls fail due to missing
 fields in the request.

Let's use less restrictive JsonInclude:NON_ABSENT annotation, which
removes only null fields. Required fields are anyway non-nullable.

Author: sathish-kumar-subramani

src/main/java/com/spotify/github/v3/checks/Annotation.java

@@ -43,7 +43,7 @@
 @Value.Immutable
 @GithubStyle
 @JsonDeserialize(as = ImmutableAnnotation.class)
-@JsonInclude(JsonInclude.Include.NON_EMPTY)
+@JsonInclude(JsonInclude.Include.NON_ABSENT)
 public interface Annotation {
 
   /**

src/test/java/com/spotify/github/v3/checks/AnnotationTest.java

@@ -24,11 +24,8 @@
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
-import com.spotify.github.FixtureHelper;
 import com.spotify.github.jackson.Json;
 import com.spotify.github.v3.checks.ImmutableAnnotation.Builder;
-import java.io.IOException;
-import java.time.ZonedDateTime;
 import org.junit.Test;
 
 public class AnnotationTest {
@@ -66,4 +63,20 @@ public void failsCreationWhenMaxLengthExceeded(){
         builder().rawDetails("a".repeat(66000)).build()
     );
   }
+
+  @Test
+  public void serializesWithEmptyFields() {
+    Annotation annotationWithEmptyStringFields = ImmutableAnnotation.builder()
+        .message("")
+        .path("")
+        .title("")
+        .startLine(1)
+        .endLine(2)
+        .annotationLevel(AnnotationLevel.notice)
+        .build();
+
+    String serializedAnnotation = Json.create().toJsonUnchecked(annotationWithEmptyStringFields);
+    String expected = "{\"path\":\"\",\"annotation_level\":\"notice\",\"message\":\"\",\"title\":\"\",\"start_line\":1,\"end_line\":2}";
+    assertThat(serializedAnnotation, is(expected));
+  }
 }