splitSignature - Undeclared identifier

[jack75015]

Hello I cloned the project and followed the step. For the compile step yarn compile, I got this error:

Downloading compiler 0.8.9
Compiling 21 files with 0.8.9
DeclarationError: Undeclared identifier.
  --> contracts/mocks/ERC1238ExpirableMock.sol:52:51:
   |
52 |                 (bytes32 r, bytes32 s, uint8 v) = splitSignature(data[i]);
   |                                                   ^^^^^^^^^^^^^^


Error HH600: Compilation failed

For more info go to https://hardhat.org/HH600 or run Hardhat with --show-stack-traces

Am i the only one?