3 files changed, 13 insertions, 2 deletions
diff --git a/lib/gitlab/import_export/json_hash_builder.rb b/lib/gitlab/import_export/json_hash_builder.rb
index 477499e1688..b145f37c052 100644
--- a/lib/gitlab/import_export/json_hash_builder.rb
+++ b/lib/gitlab/import_export/json_hash_builder.rb
@@ -67,7 +67,7 @@ module Gitlab
       # +value+ existing model to be included in the hash
       # +parsed_hash+ the original hash
       def parse_hash(value)
-        return nil if already_contains_methods?(value)
+        return if already_contains_methods?(value)
 
         @attributes_finder.parse(value) do |hash|
           { include: hash_or_merge(value, hash) }
diff --git a/lib/gitlab/import_export/merge_request_parser.rb b/lib/gitlab/import_export/merge_request_parser.rb
index 040a70d6775..deb2f59f05f 100644
--- a/lib/gitlab/import_export/merge_request_parser.rb
+++ b/lib/gitlab/import_export/merge_request_parser.rb
@@ -20,6 +20,17 @@ module Gitlab
           create_target_branch unless branch_exists?(@merge_request.target_branch)
         end
 
+        # The merge_request_diff associated with the current @merge_request might
+        # be invalid. Than means, when the @merge_request object is saved, the
+        # @merge_request.merge_request_diff won't. This can leave the merge request
+        # in an invalid state, because a merge request must have an associated
+        # merge request diff.
+        # In this change, if the associated merge request diff is invalid, we set
+        # it to nil. This change, in association with the after callback
+        # :ensure_merge_request_diff in the MergeRequest class, makes that
+        # when the merge request is going to be created and it doesn't have
+        # one, a default one will be generated.
+        @merge_request.merge_request_diff = nil unless @merge_request.merge_request_diff&.valid?
         @merge_request
       end
 
diff --git a/lib/gitlab/import_export/relation_factory.rb b/lib/gitlab/import_export/relation_factory.rb
index 099b488f68e..61a1aa6da5a 100644
--- a/lib/gitlab/import_export/relation_factory.rb
+++ b/lib/gitlab/import_export/relation_factory.rb
@@ -75,7 +75,7 @@ module Gitlab
       # the relation_hash, updating references with new object IDs, mapping users using
       # the "members_mapper" object, also updating notes if required.
       def create
-        return nil if unknown_service?
+        return if unknown_service?
 
         setup_models