The OptionValue processor can create an OptionValue without an OptionType. This can lead to problems when querying Variants which are associated with it, resulting in 500 on both Solidus API and Admin (and I'm afraid, more concerning, the Frontend).
This problem has happened quite a few times on a project I'm working on; unfortunately I haven't been able to reproduce on the sandbox yet.
There's an open pull request on Solidus addressing this problem
--
Maybe we could tweak 
  
  
    
        
          |  | option_type: option_type(i), | 
    
   
 
 so that it fails if the OptionType is 
nil ?