Use static variable from JAR file

Question

I've created a runnable JAR file which has a class with this code:

static KeysetHandle keysetHandle = null;

public String encrypt(String plainText){

    Config.register(AeadConfig.TINK_1_1_0);

       // GENERATE key
       // key generated using tink library
       keysetHandle = KeysetHandle.generateNew(AeadKeyTemplates.AES256_GCM);
}

public String decrypt(String cipherText){

    //using the key generated during encryption to decrypt
                 Aead aeadDecryption = AeadFactory.getPrimitive(keysetHandle);

} 

In my other Java application I've imported this JAR file as an external JAR file and am trying to run these methods:

import core.Crypto;

public class Sample {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Crypto crypto = new Crypto();
        System.out.println(crypto.encrypt("sampleText"));
        System.out.println(crypto.decrypt("XXX"));
    }
}

The encrypt function works as expected, but the decrypt returns a NullPointerException because keysetHandle is null. How do I get the updated value for keysetHandle?