Campaign create with plain_text Field throws wrong error

[christian-heiko]

Summary

When i set the plain_text Field on the emails array on create campaign the API returns a error and it returns a wrong one.
It says «The emails.0 field must be an array» alltough everything is set as in the API docs.

Expected Results

Both examples should work fine or return a correct error.

Actual Results

The API returns following error: «The emails.0 field must be an array»

Steps to Reproduce

<?php

use MailerLite\MailerLite;

require_once "vendor/autoload.php";

$mailerLite = new MailerLite([
    "api_key" => "",
]);

// This request works as expected:
$response = $mailerLite->campaigns->create([
    "type" => "regular",
    "name" => "My new campaign",
    "language_id" => 10,
    "emails" => [
        [
            "subject" => "My new email",
            "from_name" => "My Customer",
            "from" => "email@mycustomer.com",
            "content" => "Hello World!",
        ],
    ],
    "filter" => [],
]);

// This request throws the error that emails.0 is not set, alltough the problem is with plain_text:
$response = $mailerLite->campaigns->create([
    "type" => "regular",
    "name" => "My new campaign",
    "language_id" => 10,
    "emails" => [
        [
            "subject" => "My new email",
            "from_name" => "My Customer",
            "from" => "email@mycustomer.com",
            "content" => "Hello World!",
            "plain_text" => "Hello World!",
        ],
    ],
    "filter" => [],
]);
// PHP Fatal error:  Uncaught MailerLite\Exceptions\MailerLiteValidationException: The emails.0 field must be an array