Run-time exception (line 9): Value cannot be null.
Parameter name: key
Stack Trace:
[System.ArgumentNullException: Value cannot be null.
Parameter name: key]
at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Program.Main() :line 9