Convert EmailHelper to Kotlin

package com.fsck.k9.helper;

public final class EmailHelper {

    private EmailHelper() {}

    public static String getDomainFromEmailAddress(String email) {

        int separatorIndex = email.lastIndexOf('@');

        if (separatorIndex == -1 || separatorIndex + 1 == email.length()) {

            return null;

        }

        return email.substring(separatorIndex + 1);

    }

}

package com.fsck.k9.helper

object EmailHelper {

    @JvmStatic

    fun getDomainFromEmailAddress(email: String): String? {

        val index = email.lastIndexOf('@')

        return if (index == -1 || index == email.lastIndex) null else email.substring(index + 1)

    }

}

        assertEquals("domain", result);

    }

    @Test

    public void getDomainFromEmailAddress_withEmptyDomain_shouldReturnNull() {

        String result = EmailHelper.getDomainFromEmailAddress("user@");

        assertNull(result);

    }

}