fix broken migration abstraction, fixes restart after upgrade so the runtimestate is correct, fixes sql alter column migration to actually run if its nullable.

src/Umbraco.Infrastructure/Migrations/IncompleteMigrationExpressionException.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Runtime.Serialization;
+
+namespace Umbraco.Cms.Infrastructure.Migrations
+{
+    /// <summary>
+    /// The exception that is thrown when a migration expression is not executed.
+    /// </summary>
+    /// <remarks>
+    /// Migration expressions such as Alter.Table(...).Do() must end with Do(), else they are not executed.
+    /// When a non-executed expression is detected, an IncompleteMigrationExpressionException is thrown.
+    /// </remarks>
+    /// <seealso cref="Exception" />
+    [Serializable]
+    public class IncompleteMigrationExpressionException : Exception
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="IncompleteMigrationExpressionException" /> class.
+        /// </summary>
+        public IncompleteMigrationExpressionException()
+        { }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="IncompleteMigrationExpressionException" /> class with a message.
+        /// </summary>
+        /// <param name="message">The message that describes the error.</param>
+        public IncompleteMigrationExpressionException(string message)
+            : base(message)
+        { }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="IncompleteMigrationExpressionException" /> class.
+        /// </summary>
+        /// <param name="message">The error message that explains the reason for the exception.</param>
+        /// <param name="innerException">The exception that is the cause of the current exception, or a null reference (<see langword="Nothing" /> in Visual Basic) if no inner exception is specified.</param>
+        public IncompleteMigrationExpressionException(string message, Exception innerException)
+            : base(message, innerException)
+        { }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="IncompleteMigrationExpressionException" /> class.
+        /// </summary>
+        /// <param name="info">The <see cref="T:System.Runtime.Serialization.SerializationInfo" /> that holds the serialized object data about the exception being thrown.</param>
+        /// <param name="context">The <see cref="T:System.Runtime.Serialization.StreamingContext" /> that contains contextual information about the source or destination.</param>
+        protected IncompleteMigrationExpressionException(SerializationInfo info, StreamingContext context)
+            : base(info, context)
+        { }
+    }
+}