https://github.com/bitcoin/bitcoin/blob/9ad6f14175c19b5d47267c3dd5840c14bad43c83/src/validation.cpp#L3711

If i'm following right the flow of the code, when we hit this lane `pindex` should be always equal to nullptr thus this check may be omitted
const int maxDescendantsToVisit = 100;
        for (const auto& mi : setIterConflicting) {
            
            
            
            
            
            
            
            
            
            
            
            
            
            
            CFeeRate oldFeeRate(mi->GetModifiedFee(), mi->GetTxSize());
            if (newFeeRate <= oldFeeRate)
            {
                return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "insufficient fee",
                        strprintf("rejecting replacement %s; new feerate %s <= old feerate %s",
                            hash.ToString(),
                            newFeeRate.ToString(),
                            oldFeeRate.ToString()));
            }
            for (const CTxIn &txin : mi->GetTx().vin)
            {
                setConflictsParents.insert(txin.prevout.hash);
            }
            nConflictingCount += mi->GetCountWithDescendants();