I think you should just let this raise the normal NoMethodError.

Eg:

```ruby

def search_by_plaintext(field, criteria)
  encryptor_klass.new(crypt_keeper_options).search(all, field.to_sym, criteria)
end
```

It would be something like: `NoMethodError: undefined method `search' for #<#<Class:0x007fe71bea6b68>:0x007fe71bea6b18>`