old_contents: import jsl
  
  
  class TargetInfo(jsl.Document):
      docker = jsl.ArrayField(jsl.StringField(), max_items=2)
      rsync = jsl.ArrayField(jsl.StringField(), max_items=2)
      containers = jsl.ArrayField([
          jsl.StringField(),
          jsl.ArrayField(jsl.StringField())
      ])
  
new_contents: import jsl
  
  
  class TargetInfo(jsl.Document):
      docker = jsl.ArrayField([
          jsl.StringField(),
          jsl.OneOfField([jsl.StringField(), jsl.NullField()])
      ])
      rsync = jsl.ArrayField([
          jsl.StringField(),
          jsl.OneOfField([jsl.StringField(), jsl.NullField()])
      ])
      containers = jsl.ArrayField([
          jsl.StringField(),
          jsl.ArrayField(jsl.StringField())
      ])
  
subject: Correct the target info schema: docker and rsync messages are Null in case of success. Suggested by @vinzenz and corrected by @artmello.