Sets the value of an entry in the System.Collections.Specialized.NameValueCollection.
Type Reason NotSupportedException The current instance is read-only.
If the specified key already exists in the collection, this method overwrites the existing list of values with the specified value. To append the new value to the existing list of values, use the NameValueCollection.Add(NameValueCollection) method.
If the specified key does not exist in the collection, this method creates a new entry using the specified key and the specified value.
This method is an O(1) operation.