NFTokenBurn::preclaim should explicitly reject burn when issuer account SLE is absent

[mvadari]

Summary

In NFTokenBurn::preclaim, when a non-owner attempts to burn a burnable NFT and the issuer's account has been deleted (SLE is null), the permission check silently falls through to tesSUCCESS instead of explicitly rejecting the transaction.

Code

src/libxrpl/tx/transactors/nft/NFTokenBurn.cpp lines 35-42:

if (auto const issuer = nft::getIssuer(ctx.tx[sfNFTokenID]); issuer != account)
{
    if (auto const sle = ctx.view.read(keylet::account(issuer)); sle)
    {
        if (auto const minter = (*sle)[~sfNFTokenMinter]; minter != account)
            return tecNO_PERMISSION;
    }
    // ← if sle is null, falls through to tesSUCCESS
}

Impact

This is currently unreachable because AccountDelete::preclaim blocks deletion when sfMintedNFTokens != sfBurnedNFTokens — so the issuer's SLE can never be null while any of their NFTs exist. No exploit is possible.

However, the defensive fix is trivial: return tecNO_PERMISSION (or tecINTERNAL) when sle is null, rather than silently succeeding.

Suggested Fix

Add an else branch:

if (auto const sle = ctx.view.read(keylet::account(issuer)); sle)
{
    if (auto const minter = (*sle)[~sfNFTokenMinter]; minter != account)
        return tecNO_PERMISSION;
}
else
{
    return tecNO_PERMISSION;
}