Fixed code coverage hint

Author: Andre

lib/meilisearch/index.rb

@@ -273,10 +273,6 @@ def search(query, options = {})
 
     # document_id: Identifier of the target document
     def search_similar_documents(document_id, **options)
-      if document_id.nil? || document_id.to_s.empty?
-        raise MeiliSearch::InvalidDocumentId, 'document_id cannot be empty or nil'
-      end
-
       options.merge!(id: document_id)
       options = Utils.transform_attributes(options)