Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.data.mongodb.core.MongoTemplate]: Factory method 'getMongoTemplate' threw exception; nested exception is java.lang.IllegalArgumentException: Database name must not be empty!
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.1.2.RELEASE.jar:5.1.2.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:620) ~[spring-beans-5.1.2.RELEASE.jar:5.1.2.RELEASE]
... 55 common frames omitted
Caused by: java.lang.IllegalArgumentException: Database name must not be empty!
at org.springframework.util.Assert.hasText(Assert.java:284) ~[spring-core-5.1.2.RELEASE.jar:5.1.2.RELEASE]
at org.springframework.data.mongodb.core.MongoDbFactorySupport.<init>(MongoDbFactorySupport.java:71) ~[spring-data-mongodb-2.1.2.RELEASE.jar:2.1.2.RELEASE]
at org.springframework.data.mongodb.core.SimpleMongoDbFactory.<init>(SimpleMongoDbFactory.java:69) ~[spring-data-mongodb-2.1.2.RELEASE.jar:2.1.2.RELEASE]
at org.springframework.data.mongodb.core.SimpleMongoDbFactory.<init>(SimpleMongoDbFactory.java:59) ~[spring-data-mongodb-2.1.2.RELEASE.jar:2.1.2.RELEASE]
at org.tutoring.web.mongo.config.AbstractMongoConfig.mongoDbFactory(AbstractMongoConfig.java:23) ~[classes/:na]
at org.tutoring.web.mongo.config.PrimaryMongoConnection.getMongoTemplate(PrimaryMongoConnection.java:28) ~[classes/:na]
at org.tutoring.web.mongo.config.PrimaryMongoConnection$$EnhancerBySpringCGLIB$$c9a41f43.CGLIB$getMongoTemplate$0(<generated>) ~[classes/:na]
at org.tutoring.web.mongo.config.PrimaryMongoConnection$$EnhancerBySpringCGLIB$$c9a41f43$$FastClassBySpringCGLIB$$f5203966.invoke(<generated>) ~[classes/:na]
at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) ~[spring-core-5.1.2.RELEASE.jar:5.1.2.RELEASE]
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:363) ~[spring-context-5.1.2.RELEASE.jar:5.1.2.RELEASE]
at org.tutoring.web.mongo.config.PrimaryMongoConnection$$EnhancerBySpringCGLIB$$c9a41f43.getMongoTemplate(<generated>) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_191]
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_191]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_191]
at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_191]
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.1.2.RELEASE.jar:5.1.2.RELEASE]
... 56 common frames omitted

@Data
public abstract class AbstractMongoConfig {

//Mongo DB Properties
  private String host, database;
  private int port;

  /*
   * Method that creates MongoDbFactory
   * Common to both of the MongoDb connections
   */
  public MongoDbFactory mongoDbFactory() {
    return new SimpleMongoDbFactory(getMongoClient(), database);
  }
y dos clases, una para cada BD:

@Configuration
@EnableMongoRepositories(basePackages = {"org.tutoring.web.primary.repository"}, mongoTemplateRef = "primaryMongoTemplate")
@ConfigurationProperties(prefix = "primary.mongodb")
public class PrimaryMongoConnection extends AbstractMongoConfig {


@Primary
@Override
@Bean(name = "primaryMongoTemplate")
public MongoTemplate getMongoTemplate() {
return new MongoTemplate(mongoDbFactory());
  }
}


  private MongoClient getMongoClient() {
    return new MongoClient(host, port);
  }


  abstract public MongoTemplate getMongoTemplate();

@Configuration
@EnableMongoRepositories(
basePackages = {"org.tutoring.web.secondary.repository"},
mongoTemplateRef = "secondaryMongoTemplate")
@ConfigurationProperties(prefix = "secondary.mongodb")
public class SecondaryMongoConnection extends AbstractMongoConfig {

@Override
public
@Bean(name = "secondaryMongoTemplate")
MongoTemplate getMongoTemplate() {
  return new MongoTemplate(mongoDbFactory());
  }
}

primary.mongodb.host=127.0.0.1
primary.mongodb.port=27017
primary.mongodb.database=TutoringDb
secondary.mongodb.host=127.0.0.1
secondary.mongodb.port=27017
secondary.mongodb.database=tokensDb