Wrong bean injection of SpaceService despite correct import

Hi, Im using Confluence server in version 7.11.6 and Spring in version 5.1.7.RELEASE. I have problem with injection of SpaceService.

public class DemoClass extends SpaceAdminAction implements Serializable
{
 @ConfluenceImport
    private transient com.atlassian.confluence.api.service.content.SpaceService spaceService;  
    private String okData = null;

    @Inject
    public void setSpaceService(com.atlassian.confluence.api.service.content.SpaceService spaceService) {
        this.spaceService = spaceService;
    }
//some other stuff
}

getting this error:

org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'com.atlassian.confluence.content.service.space.DefaultSpaceService' to required type 'com.atlassian.confluence.api.service.content.SpaceService' for property 'spaceService'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'com.atlassian.confluence.content.service.space.DefaultSpaceService' to required type 'com.atlassian.confluence.api.service.content.SpaceService' for property 'spaceService': no matching editors or conversion strategy found
    at org.springframework.beans.AbstractNestablePropertyAccessor.convertIfNecessary(AbstractNestablePropertyAccessor.java:603)

caused by: java.lang.IllegalStateException: Cannot convert value of type 'com.atlassian.confluence.content.service.space.DefaultSpaceService' to required type 'com.atlassian.confluence.api.service.content.SpaceService' for property 'spaceService': no matching editors or conversion strategy found
    at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:307)

This makes no sense to me at all, since clearly, I was so desperate that I used a fully qualified name in injection to say that compiler, that I’m not trying to inject bean of
com.atlassian.confluence.content.service.SpaceService which btw is not even a bean, but the SpaceService which I’m force to use for Space lookup, since SpaceManager.getSpace is deprecated.

It looks like, that problem is related to SpaceAdminAction because in other services, this bean can be loaded without any issues.