XWIKI-19031: Computed fields are stored as empty string properties in the database

...n/java/com/xpn/xwiki/doc/DefaultDocumentAccessBridge.java

.../internal/filter/output/BaseObjectOutputFilterStream.java

...wiki/internal/objects/classes/XClassMigratorListener.java

.../java/com/xpn/xwiki/internal/store/PropertyConverter.java

...rc/main/java/com/xpn/xwiki/objects/classes/BaseClass.java

...ava/com/xpn/xwiki/objects/classes/ComputedFieldClass.java

...ain/java/com/xpn/xwiki/objects/classes/PropertyClass.java

...rc/main/java/com/xpn/xwiki/store/XWikiHibernateStore.java

.../migration/hibernate/R1008010XWIKI10092DataMigration.java