The attached sample code throws exception:

Exception in thread "main" java.security.KeyStoreException: non-null password required to create SecretKeyEntry
        at java.security.KeyStoreSpi.engineSetEntry(KeyStoreSpi.java:529)
        at java.security.KeyStore.setEntry(KeyStore.java:1285)
        at genHmacSha1.main(genHmacSha1.java:16)

According to javadoc, the 3rd param of KeyStore.setEntry could be null.

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import java.io.FileOutputStream;
import java.security.KeyStore;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;

public class genHmacSha1 {
    
    public static void main(String[] args) throws Exception {
        KeyGenerator kg = KeyGenerator.getInstance("HmacSHA1");
        SecretKey sk = kg.generateKey();

        KeyStore ks = KeyStore.getInstance("jceks");
        ks.load(null, null);
        KeyStore.SecretKeyEntry skEntry =new KeyStore.SecretKeyEntry(sk);
        ks.setEntry("HmacSHA1", skEntry, (KeyStore.ProtectionParameter)null);

        FileOutputStream fos = new FileOutputStream("hmacsha1.jceks");
        ks.store(fos, "password".toCharArray());
        fos.close();
    }
}