add nullability annotations for BRBIP32Sequence
add nullability annotations for BRBIP32Sequence

QuantumExplorer/breadwallet,thrasher-/breadwallet,QuantumExplorer/breadwallet,litecoin-association/LoafWallet,QuantumExplorer/breadwallet,litecoin-association/LoafWallet,breadwallet/breadwallet,samuraisam/breadwallet,voisine/breadwallet,voisine/breadwallet,thrasher-/breadwallet,litecoin-association/LoafWallet,voisine/breadwallet,litecoin-association/LoafWallet,samuraisam/breadwallet,breadwallet/breadwallet,breadwallet/breadwallet,samuraisam/breadwallet,QuantumExplorer/breadwallet,voisine/breadwallet,voisine/breadwallet