Options contract is marked as non-tradeable - why and how to detect it?

Ok, so far I have figured out a few things:

IsTradeable is a field on the Security class, not Symbol, so I can check that.

Option contract is marked as non-tradeable in this piece of LEAN code:

        /// <summary>
        /// Liquidate option contact holdings who's underlying security has split
        /// </summary>
        private void ProcessSplitSymbols(IAlgorithm algorithm, List<Split> splitWarnings, List<Delisting> pendingDelistings)
        {
				......
                // fetch all option derivatives of the underlying with holdings (excluding the canonical security)
                var derivatives = algorithm.Securities.Where(kvp => kvp.Key.HasUnderlying &&
                    kvp.Key.SecurityType.IsOption() &&
                    kvp.Key.Underlying == security.Symbol &&
                    !kvp.Key.Underlying.IsCanonical() &&
                    kvp.Value.HoldStock
                );

                foreach (var kvp in derivatives)
                {
   					......
                    // mark option contract as not tradable
                    optionContractSecurity.IsTradable = false;

in https://github.com/QuantConnect/Lean/blob/e7e9153fbf42a5b5d1caace8e4da7c356efff272/Engine/AlgorithmManager.cs

So I am guessing that after the split all related option contracts where there was a position are marked as non-tradeable, because option splits are not supported? Not sure the reason, but I will have to figure out some kind of work-around, perhaps liquidate options position manually before this happens.

Hmm, but there are not splits for WDFC around that date. So there should be another reason for this.

Ok, I figured that the problem was because contract was removed from the universe by expiration data and this marked it as non-tradeable. I wish I could accept my own answer :)