The given key was not present in the dictionary


I had a list column whare a value was required.
I changed this list column to allow the user to have no value on it.
Then I clicked to the link "Display setting ( powered by bewise)"
And I received the exception message posted below:
The given key was not present in the dictionary. at System.ThrowHelper.ThrowKeyNotFoundException()
at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at Bewise.SharePoint.SPListDisplaySetting.ListDisplayPage.RenderOption(SPField field, String mode, Boolean& showWhere)
at Bewise.SharePoint.SPListDisplaySetting.ListDisplayPage.RenderOptions(SPField field)
at Bewise.SharePoint.SPListDisplaySetting.ListDisplayPage.PrepareRenderPage()
at Bewise.SharePoint.SPListDisplaySetting.ListDisplayPage.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
I think you don't manage values where fileds are required then when the value change, you won't retreive the data stored for the filed you attempted to fill.