Mods to explicitly set the ObjectMapper provider (#448).

src/main/java/org/gitlab4j/api/GitLabApiClient.java

@@ -721,6 +721,9 @@ public class GitLabApiClient {
         // library to work when both Jersey and Resteasy are present
         ClientBuilder clientBuilder = new JerseyClientBuilder().withConfig(clientConfig);
 
+        // Register JacksonJson as the ObjectMapper provider.
+        clientBuilder.register(JacksonJson.class);
+
         if (ignoreCertificateErrors) {
             clientBuilder.sslContext(openSslContext).hostnameVerifier(openHostnameVerifier);
         }

src/main/java/org/gitlab4j/api/utils/JacksonJson.java

@@ -14,7 +14,6 @@ import java.util.TimeZone;
 import javax.ws.rs.Produces;
 import javax.ws.rs.core.MediaType;
 import javax.ws.rs.ext.ContextResolver;
-import javax.ws.rs.ext.Provider;
 
 import org.gitlab4j.api.models.User;
 
@@ -43,7 +42,6 @@ import com.fasterxml.jackson.jaxrs.json.JacksonJaxbJsonProvider;
 /**
  * Jackson JSON Configuration and utility class.
  */
-@Provider
 @Produces(MediaType.APPLICATION_JSON)
 public class JacksonJson extends JacksonJaxbJsonProvider implements ContextResolver<ObjectMapper> {
 
@@ -72,6 +70,8 @@ public class JacksonJson extends JacksonJaxbJsonProvider implements ContextResol
         module.addSerializer(Date.class, new JsonDateSerializer());
         module.addDeserializer(Date.class, new JsonDateDeserializer());
         objectMapper.registerModule(module);
+
+        setMapper(objectMapper);
     }
 
     @Override