Collection<> error in feature deactivation

Question

Following code shows the code when the feature gets deactivated:

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Administration; 

 public override void FeatureDeactivating(SPFeatureReceiverProperties properties)
{
    string asmDetails = typeof(OnDownload).AssemblyQualifiedName;

    SPWebApplication webApp = properties.Feature.Parent as SPWebApplication;
    if (webApp == null) return;

    List<SPWebConfigModification> configModsFound = new List<SPWebConfigModification>();
    Collection<SPWebConfigModification> modsCollection = webApp.WebConfigModifications;
    for (int i = 0; i < modsCollection.Count; i++)
    {
        if (modsCollection[i].Owner == asmDetails)
        {
            configModsFound.Add(modsCollection[i]);
        }
    }

}

I want to know why I am getting red squiggly line under this line of code

Collection<SPWebConfigModification> modsCollection = webApp.WebConfigModifications;

Answer 1

Add the reference using System.Collections.ObjectModel; to the file.