java.lang.NullPointerException: Cannot invoke "String.isEmpty()" because "pojo.asDer" is null

[ditlef9]

I am using the Java sources in Kotlin. I get the following errors on a lot of the messages:

java.lang.NullPointerException: Cannot invoke "String.isEmpty()" because "pojo.asDer" is null
	at io.calidog.certstream.CertStreamCertificate.fromPOJO(CertStreamCertificate.java:37)
	at io.calidog.certstream.CertStreamMessageData.fromPOJO(CertStreamMessageData.java:37)
	at io.calidog.certstream.CertStreamMessage.fromPOJO(CertStreamMessage.java:22)
	at io.calidog.certstream.CertStream.lambda$onMessage$1(CertStream.java:74)
	at io.calidog.certstream.CertStreamClientImplFactory$1.onMessage(CertStreamClientImplFactory.java:46)
	at io.calidog.certstream.CertStreamClientImpl.onMessage(CertStreamClientImpl.java:35)
	at org.java_websocket.client.WebSocketClient.onWebsocketMessage(WebSocketClient.java:342)
	at org.java_websocket.drafts.Draft_6455.processFrame(Draft_6455.java:599)
	at org.java_websocket.WebSocketImpl.decodeFrames(WebSocketImpl.java:370)
	at org.java_websocket.WebSocketImpl.decode(WebSocketImpl.java:202)
	at org.java_websocket.client.WebSocketClient.run(WebSocketClient.java:278)
	at java.base/java.lang.Thread.run(Thread.java:833)

This is my Main.kt:

import com.google.gson.Gson
import io.calidog.certstream.CertStream
import io.calidog.certstream.CertStreamMessage


fun main(args: Array<String>) {

    try {
        CertStream.onMessageString { x: String? ->
            if(!(x.isNullOrEmpty())){
                println(x)
            }
        }
        CertStream.onMessage { msg: CertStreamMessage? ->
            println(Gson().toJson(msg))
        }
    } catch (ex: Exception){
        print("Exeption" + ex.message)
    }
}

build.gradle.kts

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
    kotlin("jvm") version "1.6.0"
    application
}

group = "me.admin"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
    maven("https://jitpack.io")
}

dependencies {
    implementation("com.google.code.gson:gson:2.8.9")
    testImplementation(kotlin("test"))
    implementation("com.github.CaliDog:certstream-java:0.3")
}

tasks.test {
    useJUnit()
}

tasks.withType<KotlinCompile>() {
    kotlinOptions.jvmTarget = "1.8"
}

application {
    mainClass.set("MainKt")
}