Fix stock item or create

When doing a stock transfert to a stock location i get an Exception:
ActiveRecord::AssociationTypeMismatch in Spree::Admin::StockTransfersController#create
Spree::Variant(#70267740887720) expected, got String(#70267632175920)

activerecord (4.1.6) lib/active_record/associations/association.rb:216:in `raise_on_type_mismatch!'
activerecord (4.1.6) lib/active_record/associations/belongs_to_association.rb:12:in `replace'
activerecord (4.1.6) lib/active_record/associations/singular_association.rb:17:in `writer'
activerecord (4.1.6) lib/active_record/associations/builder/association.rb:118:in `variant='
activerecord (4.1.6) lib/active_record/attribute_assignment.rb:45:in `public_send'
activerecord (4.1.6) lib/active_record/attribute_assignment.rb:45:in `_assign_attribute'
activerecord (4.1.6) lib/active_record/attribute_assignment.rb:32:in `block in assign_attributes'
activerecord (4.1.6) lib/active_record/attribute_assignment.rb:26:in `each'
activerecord (4.1.6) lib/active_record/attribute_assignment.rb:26:in `assign_attributes'
activerecord (4.1.6) lib/active_record/core.rb:455:in `init_attributes'
activerecord (4.1.6) lib/active_record/core.rb:198:in `initialize'
activerecord (4.1.6) lib/active_record/inheritance.rb:30:in `new'
activerecord (4.1.6) lib/active_record/inheritance.rb:30:in `new'
activerecord (4.1.6) lib/active_record/reflection.rb:239:in `build_association'
activerecord (4.1.6) lib/active_record/associations/association.rb:247:in `build_record'
activerecord (4.1.6) lib/active_record/associations/collection_association.rb:460:in `block in _create_record'
activerecord (4.1.6) lib/active_record/associations/collection_association.rb:168:in `block in transaction'
activerecord (4.1.6) lib/active_record/connection_adapters/abstract/database_statements.rb:199:in `transaction'
activerecord (4.1.6) lib/active_record/transactions.rb:208:in `transaction'
activerecord (4.1.6) lib/active_record/associations/collection_association.rb:167:in `transaction'
activerecord (4.1.6) lib/active_record/associations/collection_association.rb:459:in `_create_record'
activerecord (4.1.6) lib/active_record/associations/collection_association.rb:137:in `create'
activerecord (4.1.6) lib/active_record/associations/collection_proxy.rb:285:in `create'
spree_core (2.3.4) app/models/spree/stock_location.rb:37:in `stock_item_or_create'
spree_core (2.3.4) app/models/spree/stock_location.rb:65:in `move'
spree_core (2.3.4) app/models/spree/stock_location.rb:49:in `restock'
spree_core (2.3.4) app/models/spree/stock_transfer.rb:28:in `block (2 levels) in transfer'
spree_core (2.3.4) app/models/spree/stock_transfer.rb:26:in `each_pair'
spree_core (2.3.4) app/models/spree/stock_transfer.rb:26:in `block in transfer'
activerecord (4.1.6) lib/active_record/connection_adapters/abstract/database_statements.rb:201:in `block in transaction'
activerecord (4.1.6) lib/active_record/connection_adapters/abstract/database_statements.rb:209:in `within_new_transaction'
activerecord (4.1.6) lib/active_record/connection_adapters/abstract/database_statements.rb:201:in `transaction'
activerecord (4.1.6) lib/active_record/transactions.rb:208:in `transaction'
activerecord (4.1.6) lib/active_record/transactions.rb:259:in `transaction'
spree_core (2.3.4) app/models/spree/stock_transfer.rb:25:in `transfer'
spree_backend (2.3.4) app/controllers/spree/admin/stock_transfers_controller.rb:31:in `create'
actionpack (4.1.6) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.1.6) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.1.6) lib/abstract_controller/callbacks.rb:20:in `block in process_action'
activesupport (4.1.6) lib/active_support/callbacks.rb:113:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:113:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:149:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:149:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:149:in `block in halting_and_conditional'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:229:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:229:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:229:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:229:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:166:in `block in halting'
activesupport (4.1.6) lib/active_support/callbacks.rb:86:in `call'
activesupport (4.1.6) lib/active_support/callbacks.rb:86:in `run_callbacks'
actionpack (4.1.6) lib/abstract_controller/callbacks.rb:19:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.1.6) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.1.6) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.1.6) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.1.6) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.1.6) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.1.6) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.1.6) lib/abstract_controller/base.rb:136:in `process'
actionview (4.1.6) lib/action_view/rendering.rb:30:in `process'
actionpack (4.1.6) lib/action_controller/metal.rb:196:in `dispatch'
actionpack (4.1.6) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.1.6) lib/action_controller/metal.rb:232:in `block in action'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:82:in `call'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:82:in `dispatch'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:50:in `call'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:73:in `block in call'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:678:in `call'
railties (4.1.6) lib/rails/engine.rb:514:in `call'
railties (4.1.6) lib/rails/railtie.rb:194:in `public_send'
railties (4.1.6) lib/rails/railtie.rb:194:in `method_missing'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:73:in `block in call'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.1.6) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.1.6) lib/action_dispatch/routing/route_set.rb:678:in `call'
warden (1.2.3) lib/warden/manager.rb:35:in `block in call'
warden (1.2.3) lib/warden/manager.rb:34:in `catch'
warden (1.2.3) lib/warden/manager.rb:34:in `call'
rack (1.5.2) lib/rack/etag.rb:23:in `call'
rack (1.5.2) lib/rack/conditionalget.rb:35:in `call'
rack (1.5.2) lib/rack/head.rb:11:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/flash.rb:254:in `call'
rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/cookies.rb:560:in `call'
activerecord (4.1.6) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.1.6) lib/active_record/connection_adapters/abstract/connection_pool.rb:621:in `call'
activerecord (4.1.6) lib/active_record/migration.rb:380:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.1.6) lib/active_support/callbacks.rb:82:in `run_callbacks'
actionpack (4.1.6) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/reloader.rb:73:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.1.6) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.1.6) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.1.6) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.1.6) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.1.6) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.1.6) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.1.6) lib/active_support/cache/strategy/local_cache_middleware.rb:26:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.1.6) lib/action_dispatch/middleware/static.rb:64:in `call'
rack (1.5.2) lib/rack/sendfile.rb:112:in `call'
railties (4.1.6) lib/rails/engine.rb:514:in `call'
railties (4.1.6) lib/rails/application.rb:144:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
puma (2.9.2) lib/puma/server.rb:490:in `handle_request'
puma (2.9.2) lib/puma/server.rb:361:in `process_client'
puma (2.9.2) lib/puma/server.rb:254:in `block in run'
puma (2.9.2) lib/puma/thread_pool.rb:92:in `call'
puma (2.9.2) lib/puma/thread_pool.rb:92:in `block in spawn_thread'
logging (1.8.2) lib/logging/diagnostic_context.rb:323:in `call'
logging (1.8.2) lib/logging/diagnostic_context.rb:323:in `block in create_with_logging_context'

Here is a fix.