Hi everyone! When I try to compile contract I get this error

error: undefined function `slice_empty?`, defining a global function of unknown type
if (slice_empty?(in_msg)) {
^
( function `slice_empty?` undefined )

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my method of contract is

() recv_external(slice in_msg) impure {
if (slice_empty?(in_msg)) {
return ();
}
}

-------------------

and command I run to compile ./crypto/func -APSR -o ./new_pr/build/compiled.fif ./new_pr/code.fc

What's wrong?