refactor: convert responseCodeExtractor class from java to kotlin

package com.fsck.k9.mail.store.imap;

package com.fsck.k9.mail.store.imap

internal object ResponseCodeExtractor {

    const val AUTHENTICATION_FAILED: String = "AUTHENTICATIONFAILED"

class ResponseCodeExtractor {

    public static final String AUTHENTICATION_FAILED = "AUTHENTICATIONFAILED";

    private ResponseCodeExtractor() {

    }

    public static String getResponseCode(ImapResponse response) {

        if (response.size() < 2 || !response.isList(1)) {

            return null;

    @JvmStatic

    fun getResponseCode(response: ImapResponse): String? {

        if (response.size < 2 || !response.isList(1)) {

            return null

        }

        ImapList responseTextCode = response.getList(1);

        return responseTextCode.size() != 1 ? null : responseTextCode.getString(0);

        val responseTextCode = response.getList(1)

        return if (responseTextCode.size != 1) null else responseTextCode.getString(0)

    }

}