Steps to reproduce

• Create a content type with a multiple content attribute
• Add a default value to this attribute like pointing to an unexisting content:

  <default-value type="attribute" name="code">WRONG</default-value>

• Try to create or edit a content with this content type
• You get an error message with no link with the real error. It is an NPE at line 237 of org.ametys.cms.data.type.AbstractContentElementType. It is caused by an array with one null element due to org.ametys.runtime.model.DefaultElementDefinition.getDefaultValue()

If the attribute is multiple, we create an array of number of theorical default values.
But our value is null here, so we get an array with a null element.

NB : This case can occur while using other data than the client data or if an element have been deleted.