Possible to create a domain class that is NOT mapped to a database table

I'm using Grails 1.2.1. I'm converting a Java app to a Grails app and I had a Java object that I thought I'd create a grails domain for. However, the object does not rely on an underlying database table. When I startup my app, I'm getting the error,

ERROR context.ContextLoader – Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'messageSource': Initialization of bean
failed; nested exception is
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'transactionManager': Cannot resolve reference
to bean 'sessionFactory' while setting bean property 'sessionFactory';
nested exception is
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'sessionFactory': Invocation of init method
failed; nested exception is org.hibernate.MappingException: Could not
determine type for: java.io.InputStream, at table:
http_cache_response, for columns: [org.hibernate.mapping.Column(body)]

Am I misusing the domain? Should this object just be a regular class in src/groovy? Thanks, – Dave