java.lang.NullPointerException while trying to handshake for SSLSocket

Question

I need to establish a secure socket connection on Java/Kotlin.

The server gave me 2 files:

1. The CA certificate.
2. The server key in the "pem" format.

I converted both keys to the JKS format using the portecle.

For some reason the java.lang.NullPointerException occurs during the handshake. OpenJDK crashes here. Here is my source code:

class Connection(
        val host: String,
        val port: Int
)

class KeyStoreParams(
        val inputStream: InputStream,
        val password: String
)

class SocketClient(
        private val connection: Connection,
        private val keyStoreParams: KeyStoreParams,
        private val trustStoreParams: KeyStoreParams
) {
    companion object {
        private val sslContextType = "TLS"
        private var keyStoreType = "JKS"
    }

    fun connect() {
        val sslContext = SSLContext.getInstance(sslContextType)
        sslContext.init(getKeyManagers(), getTrustManagers(), SecureRandom())

        val socket = sslContext.socketFactory.createSocket(connection.host, connection.port) as SSLSocket
        socket.startHandshake()
    }

    private fun getKeyManagers(): Array<KeyManager> {
        val keyStore = getKeyStore(keyStoreParams.inputStream, keyStoreParams.password)

        val keyManagerAlgorithm = KeyManagerFactory.getDefaultAlgorithm()
        val keyManagerFactory = KeyManagerFactory.getInstance(keyManagerAlgorithm)
        keyManagerFactory.init(keyStore, keyStoreParams.password.toCharArray())

        return keyManagerFactory.keyManagers
    }

    private fun getTrustManagers(): Array<TrustManager> {
        val keyStore = getKeyStore(trustStoreParams.inputStream, trustStoreParams.password)

        val trustManagerAlgorithm = TrustManagerFactory.getDefaultAlgorithm()
        val trustManagerFactory = TrustManagerFactory.getInstance(trustManagerAlgorithm)
        trustManagerFactory.init(keyStore)

        return trustManagerFactory.trustManagers
    }

    private fun getKeyStore(inputStream: InputStream, password: String): KeyStore {
        val keyStore = KeyStore.getInstance(keyStoreType)
        keyStore.load(inputStream, password.toCharArray())
        inputStream.close()

        return keyStore
    }
}

fun connect() {
    val connection = Connection(host, port)
    val keyStoreParams = KeyStoreParams(streamForFile(keyStorePath), keyStorePassword)
    val trustStoreParams = KeyStoreParams(streamForFile(trustStorePath), trustStorePassword)

    val client = SocketClient(connection, keyStoreParams, trustStoreParams)
    client.connect()
}

private fun streamForFile(path: String): InputStream {
    return javaClass.classLoader.getResource(path)!!.openStream()
}

Here is the stacktrace:

Exception in thread "main" javax.net.ssl.SSLException
    at java.base/sun.security.ssl.Alert.createSSLException(Alert.java:133)
    at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:325)
    at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:268)
    at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:263)
    at java.base/sun.security.ssl.SSLSocketImpl.handleException(SSLSocketImpl.java:1667)
    at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:454)
    at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:412)
    at com.example.test.network.socket.SocketClient.connect(SocketClient.kt:23)
    at com.example.test.network.NetworkManager.connect(NetworkManager.kt:24)
    at MainKt.main(main.kt:5)
    at MainKt.main(main.kt)
Caused by: java.lang.NullPointerException
    at java.base/sun.security.ssl.CertificateRequest$ClientCertificateType.getKeyTypes(CertificateRequest.java:136)
    at java.base/sun.security.ssl.CertificateRequest$T10CertificateRequestMessage.getKeyTypes(CertificateRequest.java:199)
    at java.base/sun.security.ssl.CertificateRequest$T10CertificateRequestConsumer.consume(CertificateRequest.java:365)
    at java.base/sun.security.ssl.SSLHandshake.consume(SSLHandshake.java:396)
    at java.base/sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:445)
    at java.base/sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:423)
    at java.base/sun.security.ssl.TransportContext.dispatch(TransportContext.java:182)
    at java.base/sun.security.ssl.SSLTransport.decode(SSLTransport.java:171)
    at java.base/sun.security.ssl.SSLSocketImpl.decode(SSLSocketImpl.java:1475)
    at java.base/sun.security.ssl.SSLSocketImpl.readHandshakeRecord(SSLSocketImpl.java:1381)
    at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:441)
    ... 5 more

Thanks!