Add NON_ABSENT to MergeParams (#17)

* Add NON_ABSENT to MergeParams

* update header

Author: henriquetruta

src/main/java/com/spotify/github/v3/prs/MergeParameters.java

@@ -20,6 +20,7 @@
 
 package com.spotify.github.v3.prs;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import com.fasterxml.jackson.databind.annotation.JsonSerialize;
 import com.spotify.github.GithubStyle;
@@ -35,6 +36,7 @@
 @GithubStyle
 @JsonSerialize(as = ImmutableMergeParameters.class)
 @JsonDeserialize(as = ImmutableMergeParameters.class)
+@JsonInclude(JsonInclude.Include.NON_ABSENT)
 public abstract class MergeParameters {
   /**
    * SHA that pull request head must match to allow merge.

src/test/java/com/spotify/github/v3/prs/PullRequestTest.java

@@ -62,4 +62,20 @@ public void testSerializationMergeParams() throws IOException {
     assertThat(params.sha(), is(fixtureParams.sha()));
     assertThat(params.mergeMethod(), is(MergeMethod.merge));
   }
+
+  @Test
+  public void testDeserializationMergeParamsOmitsFields() throws IOException {
+    final MergeParameters params = ImmutableMergeParameters.builder()
+        .commitMessage("a message")
+        .sha("6dcb09b5b57875f334f61aebed695e2e4193db5e")
+        .build();
+    final String json = Json.create().toJson(params);
+
+    assertThat(
+        json,
+        is(
+            "{\"sha\":\"6dcb09b5b57875f334f61aebed695e2e4193db5e\",\"commit_message\":\"a message\",\"merge_method\":\"merge\"}"));
+
+    System.out.println(json);
+  }
 }