getCollection fails in starting mongo session

I am trying to build unit tests for a spring boot app and its failing creating a session. Here's the code

abstract class AbstractFongoBaseConfiguration extends AbstractMongoConfiguration {

  Logger log = Logger.getLogger(AbstractFongoBaseConfiguration)

  @Autowired
  private Environment env

  @Override
  protected String getDatabaseName() {
    return env.getRequiredProperty("spring.data.mongodb.database")
  }

  @Override
  MongoClient mongoClient() throws Exception {
    log.info("MongoClient mongoClient() ")
    return new Fongo("fongo server 2").mongo
  }

  @Bean
  Mongo mongo() {
    log.info("Mongo mongo()")
    return new Fongo("fongo server 1").mongo
  }
}

@EnableAutoConfiguration(exclude = [ EmbeddedMongoAutoConfiguration, MongoAutoConfiguration,
  MongoDataAutoConfiguration ])
@Configuration
//@ComponentScan(basePackages = ["com.isolisduran.springboot" ], excludeFilters = [
//  @ComponentScan.Filter(classes = RufusEngineApp ) ])
class ConfigServerWithFongoConfiguration extends AbstractFongoBaseConfiguration {

}


@SpringBootTest(classes = [ConfigServerWithFongoConfiguration, RufusEngineApp],
    properties = "server.port=8980",
    webEnvironment = SpringBootTest.WebEnvironment.DEFINED_PORT)
@AutoConfigureMockMvc
@TestPropertySource(properties = "spring.data.mongodb.database=test" )
@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
//@SpringBootTest(classes = RufusEngineApp)
class MongoDbSpringIntegrationTest extends Specification {

  @Autowired
  @Qualifier("inventoryCollection")
  MongoCollection inventory

  void test() {
    setup:
    DBObject objectToSave = BasicDBObjectBuilder.start()
        .add("key", "value")
        .get()

    when:
    inventory.save(objectToSave)

    then:
    inventory.find().extracting("key").containsOnly("value")
  }
}

and the applications jongo class is

@Configuration
@ConditionalOnClass([Jongo])
class JongoAutoConfiguration {

  Logger log = Logger.getLogger(JongoAutoConfiguration)

  @Autowired
  protected Mongo mongo

  DB rufusdb

  @Autowired
  protected MongoProperties properties

  @Bean
  DB rufusdb() {
    this.rufusdb = mongo.getDB(properties.database)
    return this.rufusdb
  }

  private Jongo getJongoDBObject() {
    if (this.rufusdb == null) {
      rufusdb()
    }

    if (rufusdb == null) {
      log.error("rufudb is null")
    } else {
      log.error("rufudb is not null")
    }

    Mapper mapper = new JacksonMapper.Builder()
      .registerModule(new JodaModule())
      .enable(MapperFeature.AUTO_DETECT_GETTERS)
      .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
      .build()

    return new Jongo(this.rufusdb, mapper)
  }

  @Bean
  Jongo jongoConnection() {
    getJongoDBObject()
  }

  @Bean
  @DependsOn("rufusdb")
  MongoCollection inventoryCollection() {
    Jongo dbtmp = getJongoDBObject()

    dbtmp.getCollection("inventory")
  }

  @Bean
  @DependsOn("rufusdb")
  MongoCollection configCollection() {
    getJongoDBObject().getCollection("config")
  }

}

and when i run it, i get this error:

Caused by: java.lang.NullPointerException: null
    at com.mongodb.Mongo.createClientSession(Mongo.java:870) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.Mongo$3.getClientSession(Mongo.java:862) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.Mongo$3.execute(Mongo.java:819) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.Mongo$3.execute(Mongo.java:809) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.DBCursor.initializeCursor(DBCursor.java:870) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.DBCursor.hasNext(DBCursor.java:141) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.DBCursor.one(DBCursor.java:679) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.DBCollection.findOne(DBCollection.java:829) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.DBCollection.findOne(DBCollection.java:792) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.DBCollection.findOne(DBCollection.java:739) ~[mongo-java-driver-3.6.1.jar:na]
    at com.mongodb.FongoDBCollection.createIndex(FongoDBCollection.java:522) ~[fongo-2.1.1.jar:na]
    at com.mongodb.FongoDBCollection.<init>(FongoDBCollection.java:93) ~[fongo-2.1.1.jar:na]
    at com.mongodb.FongoDB.doGetCollection(FongoDB.java:96) ~[fongo-2.1.1.jar:na]
    at com.mongodb.FongoDB.doGetCollection(FongoDB.java:87) ~[fongo-2.1.1.jar:na]
    at com.mongodb.FongoDB.getCollection(FongoDB.java:82) ~[fongo-2.1.1.jar:na]
    at com.mongodb.FongoDB.getCollection(FongoDB.java:32) ~[fongo-2.1.1.jar:na]
    at org.jongo.Jongo.getCollection(Jongo.java:42) ~[jongo-1.4.0.jar:na]
    at org.jongo.Jongo$getCollection.call(Unknown Source) ~[na:na]
    at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48) ~[groovy-all-2.4.12.jar:2.4.12]
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113) ~[groovy-all-2.4.12.jar:2.4.12]
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125) ~[groovy-all-2.4.12.jar:2.4.12]
    at com.highmark.rufus.engine.JongoAutoConfiguration.inventoryCollection(JongoAutoConfiguration.groovy:70) ~[main/:na]
    at com.highmark.rufus.engine.JongoAutoConfiguration$$EnhancerBySpringCGLIB$$86294ec4.CGLIB$inventoryCollection$5(<generated>) ~[main/:na]
    at com.highmark.rufus.engine.JongoAutoConfiguration$$EnhancerBySpringCGLIB$$86294ec4$$FastClassBySpringCGLIB$$1588289d.invoke(<generated>) ~[main/:na]
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:361) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at com.highmark.rufus.engine.JongoAutoConfiguration$$EnhancerBySpringCGLIB$$86294ec4.inventoryCollection(<generated>) ~[main/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_161]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_161]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_161]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_161]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 94 common frames omitted

fakemongo / fongo

getCollection fails in starting mongo session #348