I updated an umbraco site from v7.2.6 to v7.5.14 via NuGet. The update went fine and the column securityStampToken is added to the umbracoUser table. All entries inside that table have a NULL value in the securityStampToken column.

Now I went from v7.5.14 to v7.11.1, but I'm unable to login to the back-office when the update wizard is shown. An exception is thrown:

  "Message": "An error has occurred.",
  "ExceptionMessage": "Value cannot be null.
Parameter name: value",
  "ExceptionType": "System.ArgumentNullException",
  "StackTrace": "   at System.Security.Claims.Claim..ctor(String type, String value, String valueType, String issuer, String originalIssuer, ClaimsIdentity subject, String propertyKey, String propertyValue)
   at System.Security.Claims.Claim..ctor(String type, String value, String valueType, String issuer, String originalIssuer, ClaimsIdentity subject)
   at Umbraco.Core.Security.UmbracoBackOfficeIdentity.AddUserDataClaims()
   at Umbraco.Core.Security.UmbracoBackOfficeIdentity..ctor(ClaimsIdentity claimsIdentity, UserData userdata)
   at Umbraco.Core.Security.BackOfficeClaimsIdentityFactory`1.<CreateAsync>d__3.MoveNext()"

I attached the umbraco source and it fails on this line: https://github.com/umbraco/Umbraco-CMS/blob/cbd5071eed98e6ee65506c7347d96239e7ca50af/src/Umbraco.Core/Security/UmbracoBackOfficeIdentity.cs#L230

//The security stamp claim is also required... this is because this claim type is hard coded
// by the SecurityStampValidator, see: https://katanaproject.codeplex.com/workitem/444
if (HasClaim(x => x.Type == Microsoft.AspNet.Identity.Constants.DefaultSecurityStampClaimType) == false)
    AddClaim(new Claim(Microsoft.AspNet.Identity.Constants.DefaultSecurityStampClaimType, SecurityStamp, ClaimValueTypes.String, Issuer, Issuer, this));

So there are 2 possibilities: the securityStampToken is NULL but it shouldn't, or the login needs a securityStampToken while it may be NULL.