for a long time the private key '0000000000000000000000000000000000000000000000000000000000000000'
had lots of btc, but I notice now its gone, you used to not be able to use that address, so they patched the code enabled and somebody swept the address
That private key is invalid, has no associated public key, and therefore has no associated address. What address are you looking at that you think has been swept?
This address is also a 'burn', as there is an hash160 of all zeros, or if there was it would take an infinite amount of time to find that hash that only contained zero's.
Even if someone found a hash collision for this address (or any address, for that matter), the would only obtain that address's public key, and would still have to solve the ECDLP to find the private key.
Your missing the point, that address for private key all zeros, used to be an invalid address, while 'ku' can't generate the address you can by using ecdsa algos yourself, I noticed last year that the address now had a zero balance, so somebody modified bitcoin internals to accept that addresss,
pk = k * G ( = zero )
y^2=x^3+7
secp256k1, [0,7]
There is a real value for the zero priv-key 'k', it can be calculated, but before last year the address had value, now its gone; so somebody inside of bitcoin-core-dev hacked the code to enable cashing out that address.
There is also the brainwallet key from the null-string "" that generated a non-usable address.
There used to be lots of funny addresses that couldn't be used, all seem to have been enabled in recent years.
Only one that remains & I dont' think anybody on earth has the priv-key to generate a public-key when hashed that is all zero's.
... here the sha256 (public-key) -> all zeros
now the only address that still has a balance is hash160 all zero bitcoin-address.
hash160 : 0000000000000000000000000000000000000000
Bitcoin address : 1111111111111111111114oLvT2
At 95k transactions it used to be a dust account, now at 198.2 btc, but nobody knows the 'private-key' for this puppy, so its a real burn address, as anything sent to this address is going to stay there forever