Pastable version of IEnumerable<> comparision extension method

<pre class='prettyprint' language='cs'>/// &lt;summary&gt;
/// Compares the content of two enumerables for equality. Order
/// of elements does NOT matter. Elements may exist multiple
/// times. &lt;c&gt;null&lt;/c&gt; is both a valid key and value.
/// 
/// O(n). Fast for elements with well distributed hashcode.
/// &lt;/summary&gt;
public static bool ContentEquals&lt;T&gt; (
	this IEnumerable&lt;T&gt; first,
	IEnumerable&lt;T&gt; second,
	IEqualityComparer&lt;T&gt; comparer)
{
	// Declare a dictionary to count the occurence of the items in the collection			
	Dictionary&lt;T, int&gt; itemCounts = new Dictionary&lt;T, int&gt; (comparer);

// null references are stored here.
	int zero = 0;

// Increase the count for each occurence of the item in the first collection
	foreach (T item in first) {
		if (item == null) {
			zero++;
		}
		else if (itemCounts.ContainsKey (item)) {
			itemCounts[item]++;
		}
		else {
			itemCounts[item] = 1;
		}
	}

// Decrease the count for each occurence of the item in the second collection
	foreach (T item in second) {
		if (item == null) {
			zero--;
		}
		else if (itemCounts.ContainsKey (item)) {
			itemCounts[item]--;
		}
		else {
			// There was no occurence of this item in the first collection, thus the collections are not equal
			return false;
		}
	}

// The count of each item should be 0 if the contents of the collections are equal
	foreach (int value in itemCounts.Values) {
		if (value != 0) {
			return false;
		}
	}
	if (zero != 0) {
		return false;
	}

// The collections are equal
	return true;
}</pre>
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Pastable version of IEnumerable<> comparision extension method