title: Why does a Spring's FactoryBean getObject return null?
body: <p>I want to create a Spring <code>ConversionService</code> with custom <code>Converter</code>s, but the return value of <code>ConversionServiceFactoryBean#getObject</code> is <code>null</code>. See example:</p>
  
  <pre><code>@Bean
  @Autowired
  public ConversionService conversionService(Set&lt;Converter&lt;?, ?&gt;&gt; converters) {
      final ConversionServiceFactoryBean factory = new ConversionServiceFactoryBean();
      factory.setConverters(converters);
      return checkNotNull(
              factory.getObject(),
              "conversionService must not be null.");
  }
  </code></pre>
  
  <p><code>checkNotNull</code> throws a <code>NullPointerException</code>. The <code>converters</code> are injected as expected. Why does the factory return <code>null</code>? How can I fix that?</p>