Assertion for public key to be null makes no sense

My code:
```
val keyProvider = ssh.loadKeys(config.privateKey, config.publicKey, null)
```

Error:
```
java.lang.AssertionError
at net.schmizz.sshj.userauth.keyprovider.BaseFileKeyProvider.init(BaseFileKeyProvider.java:62)
at net.schmizz.sshj.userauth.keyprovider.BaseFileKeyProvider.init(BaseFileKeyProvider.java:68)
at net.schmizz.sshj.SSHClient.loadKeys(SSHClient.java:622)
```

Code that produces error:
```
package net.schmizz.sshj.userauth.keyprovider;

@Override
public void init(String privateKey, String publicKey) {
assert privateKey != null;
assert publicKey == null; // <------------------------------------ why does it matter if it is null?
resource = new PrivateKeyStringResource(privateKey);
```

Why is there an assertions for publickey to be null?