Merge pull request #1955 from scireum/SIRI-939_kba_nullable

Properly marks field as nullable

src/main/java/sirius/biz/tycho/kb/KnowledgeBaseEntry.java

@@ -94,6 +94,7 @@ public class KnowledgeBaseEntry extends SearchableEntity {
      * Contains a short and concise description of this article.
      */
     public static final Mapping DESCRIPTION = Mapping.named("description");
+    @NullAllowed
     @SearchContent
     private String description;