CCM NG/ccm-core: MimeTypeConverter now works with null values for the MimeType in the database

git-svn-id: https://svn.libreccm.org/ccm/ccm_ng@4884 8810af33-2d31-482b-a856-94f89814c4df

ccm-core/src/main/java/org/libreccm/jpa/utils/MimeTypeConverter.java

@@ -43,6 +43,9 @@ public class MimeTypeConverter implements AttributeConverter<MimeType, String> {
 
     @Override
     public MimeType convertToEntityAttribute(final String dbData) {
+        if (dbData == null) {
+            return null;
+        }
         try {
             return new MimeType(dbData);
         } catch (MimeTypeParseException ex) {