Issue saving umbraco document, forms workflow

[jesperlange]

There is a form with a dropdown, the content in the dropdown is set from prevalues. Those prevalues are based on a document type which has a content picker.
The workflow from the form creates a content node when saving. When that gets saved and stored in backoffice, you get an error - because of the content picker.

Step by step to reproduce

Here's the form with the workflows.

The prevalues are created from this generic document type

The workflow is based of a document type:

Which looks like this:

The content picker in the document type looks like this:

When it's all setup, and you fill out the form on front-end, you get this error when you log into backoffice.

`An error occured
Multiple actions were found that match the request: GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController

Exception Details
System.InvalidOperationException: Multiple actions were found that match the request: GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController
Stacktrace
at System.Web.Http.Controllers.ApiControllerActionSelector.ActionSelectorCacheItem.SelectAction(HttpControllerContext controllerContext)
at Umbraco.Web.Editors.ParameterSwapControllerActionSelector.SelectAction(HttpControllerContext controllerContext)
at System.Web.Http.ApiController.ExecuteAsync(HttpControllerContext controllerContext, CancellationToken cancellationToken)
at System.Web.Http.Dispatcher.HttpControllerDispatcher.d__1.MoveNext()`

Bug summary

The api call in the backend, to get data stored in the picker fails due to wrong type of data stored on the property.

Specifics

Where applicable:

• What version are you using
  Umbraco 7.14.0
  Forms 7.1.3
• What browser and version you are using
  Chrome
  • Please mention if you've checked it in other browsers as well
    I have not

Steps to reproduce

Already posted.

Expected result

* What did you _expect_ that would happen on your site?

Being able to pick some content in the content picker without - but instead get immediate error.
after closing the error you can pick content, but it wont saved the content you picked.
* Describe the intended/desired outcome after you did the steps mentioned.
Being able to pick content in the created content node and save it.

Actual result

`An error occured
Multiple actions were found that match the request: GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController

Exception Details
System.InvalidOperationException: Multiple actions were found that match the request: GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController GetByIds on type Umbraco.Web.Editors.EntityController
Stacktrace
at System.Web.Http.Controllers.ApiControllerActionSelector.ActionSelectorCacheItem.SelectAction(HttpControllerContext controllerContext)
at Umbraco.Web.Editors.ParameterSwapControllerActionSelector.SelectAction(HttpControllerContext controllerContext)
at System.Web.Http.ApiController.ExecuteAsync(HttpControllerContext controllerContext, CancellationToken cancellationToken)
at System.Web.Http.Dispatcher.HttpControllerDispatcher.d__1.MoveNext()`

[nul800sebastiaan]

This is the same problem as #156

There's more info in #162 with the advise not to use a content picker (I think that's the conclusion, not sure?).