Migration results in "Sequence contains no elements" error

I created a model with 3 classes using table-per-hierarchy inheritance, and with 2 foreign keys that self reference the hierarchy table. I have a `BaseProperty` class with a self referencing key `CloneID` and navigation property `Clone`: ``` public class BaseProperty { public int ID {get; set; } public int? CloneID {get; set; } public BaseProperty Clone {get; set; } //If I add this code, when I use Add-Migration - //Sequence contains no elements error //public int? TriggeredCloneID {get; set;} } ``` I have a `Property` class that inherits `BaseProperty` and has a foreign key `BlockID` and a `Block` navigation property. ``` public class Property : BaseProperty { public int? BlockID { get; set; } public Block { get; set; } } ``` I have a `Block` class that inherits `BaseProperty` and has a `Properties` navigation property: ``` public class Block: BaseProperty { public ICollection<Property> Properties { get; set; } [DatabaseGenerated(DatabaseGeneratedOption.Computed)] public int? ComputedNumberOfProperties { get; set; } } ``` Note that the `Block` property in the `Property` class is also self referencing because both `Property` and `Block` inherit `BaseProperty` and I am using table-per-hierarchy inheritance. It has been working and is in a production system with live data. Now I want to add a field (just a standard `int?` property) to the base class and I get a "Sequence contains no elements" error when I add a migration. I found the open issue at https://entityframework.codeplex.com/workitem/569, so I tried the workaround described and removed the self-referencing keys and navigation properties, but that migration failed with the same error. I now appear to be completely skewered...