I updated my site from EPiServer CMS 6 to EPiServer CMS 7 and when I'm trying to run it, the site throws an exception -> .EPiServerException: A value is required for pageReference .

This error occured in line code below;

protected override bool ConvertToExternalInternal(EPiServer.UrlBuilder url, object internalObject, System.Text.Encoding toEncoding)
{
    if (base.ConvertToExternalInternal(url, internalObject, toEncoding))
    {
        url.Path = url.Path.ToLower();
        return true;
    }
    return false;
}

Below is the complete stack trace of Exception: 

[EPiServerException: A value is required for pageReference]
   EPiServer.Web.FriendlyUrlRewriteProvider.GetFriendlyPagePath(PageReference pageReference, String currentLanguageBranch, IContentRepository contentRepository, IPermanentLinkMapper permanentLinkMapper, ILanguageBranchRepository languageBranchRepository) +873
   EPiServer.Web.FriendlyUrlRewriteProvider.GetFriendlyPagePath(PageReference pageReference, String currentLanguageBranch) +117
   EPiServer.Web.FriendlyUrlRewriteProvider.ConvertToExternalInternal(UrlBuilder url, Object internalObject, Encoding toEncoding) +264
   eman.Public.EmanHelper.LowerCaseUrlRewriteProvider.ConvertToExternalInternal(UrlBuilder url, Object internalObject, Encoding toEncoding) in C:\egenita\web apps\e-man\WebUI\EmanHelper\LowerCaseUrlRewriteProvider.cs:27
   EPiServer.Web.FriendlyUrlRewriteProvider.ConvertToExternal(UrlBuilder url, Object internalObject, Encoding toEncoding) +177
   EPiServer.Web.FriendlyHtmlRewriteToExternal.HtmlRewriteUrl(UrlBuilder internalUrl, UrlBuilder externalUrl, UrlBuilder url, Encoding encoding, RebaseAction rebase, Object& internalObject) +76
   EPiServer.Web.FriendlyHtmlRewriteToExternal.rewritePipe_HtmlRewriteUrl(Object sender, HtmlRewriteEventArgs e) +397
   EPiServer.Web.RewritePipe.OnHtmlRewriteUrl(HtmlRewriteEventArgs e) +19
   EPiServer.Web.HtmlRewritePipe.WriteElement(MyHtmlRewriteEventArgs e, SgmlReader reader, TextWriter writer) +485
   EPiServer.Web.HtmlRewritePipe.RewriteToEnd(TextReader reader, TextWriter writer) +2277
   EPiServer.Web.HtmlRewriteStream.Close() +177
   System.Web.HttpWriter.FilterIntegrated(Boolean finalFiltering, IIS7WorkerRequest wr) +195
   System.Web.HttpResponse.FilterOutput() +159
   System.Web.CallFilterExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +52
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

Help me guys to ressolve this problem. Thanks