Argument 1 passed to MagentoFrameworkMailAddressConverter::convertMany() must be of the type array, null given,

I have created a pop up html form for sending mail to admin panel, it can pop up and keys in data but somehow it showed error while submitting.

app/code/Myvendor/Mymodule/Block/Popup.php

<?php

namespace MyvendorMymoduleBlock;

use MagentoFrameworkViewElementTemplate;

class Popup extends MagentoFrameworkViewElementTemplate
{
protected $_registry;

public function __construct(TemplateContext $context, array $data = [], MagentoFrameworkRegistry $registry)
{
    $this->_registry = $registry;
    parent::__construct($context, $data);
}

public function _prepareLayout()
{
    return parent::_prepareLayout(); // TODO: Change the autogenerated stub
}

public function getCurrentCategory() {
    return $this->_registry->registry('current_category');
}

public function getCurrentProduct() {
    return $this->_registry->registry('current_product');
}


/**
 * @return string
 */
  public function getFormAction()
  {

    return $this->getUrl('productenquiry/index/send', ['_secure' => true]);
  }
}

app/code/Myvendor/Mymodule/Controller/Index/Send.php

<?php
namespace MyvendorMymoduleControllerIndex;
use MagentoFrameworkAppActionContext;
use MagentoFrameworkMailTemplateTransportBuilder;
use Zend_Mail_Transport_Sendmail;

class Send extends MagentoFrameworkAppActionAction{

/**
 * Recipient email config path
 */
const XML_PATH_EMAIL_RECIPIENT = 'email_section/sendmail/email_section_sendmail_email_template';
/**
 * @var MagentoFrameworkMailTemplateTransportBuilder
 */
protected $_transportBuilder;

/**
 * @var MagentoFrameworkTranslateInlineStateInterface
 */
protected $inlineTranslation;

/**
 * @var MagentoFrameworkAppConfigScopeConfigInterface
 */
protected $scopeConfig;

/**
 * @var MagentoStoreModelStoreManagerInterface
 */
protected $storeManager;
/**
 * @var MagentoFrameworkEscaper
 */
protected $_escaper;
/**
 * @param MagentoFrameworkAppActionContext $context
 * @param MagentoFrameworkMailTemplateTransportBuilder $transportBuilder
 * @param MagentoFrameworkTranslateInlineStateInterface $inlineTranslation
 * @param MagentoFrameworkAppConfigScopeConfigInterface $scopeConfig
 * @param MagentoStoreModelStoreManagerInterface $storeManager
 */
public function __construct(
    MagentoFrameworkAppActionContext $context,
    MagentoFrameworkMailTemplateTransportBuilder $transportBuilder,
    MagentoFrameworkTranslateInlineStateInterface $inlineTranslation,
    MagentoFrameworkAppConfigScopeConfigInterface $scopeConfig,
    MagentoStoreModelStoreManagerInterface $storeManager,
    MagentoFrameworkEscaper $escaper
) {
    parent::__construct($context);
    $this->_transportBuilder = $transportBuilder;
    $this->inlineTranslation = $inlineTranslation;
    $this->scopeConfig = $scopeConfig;
    $this->storeManager = $storeManager;
    $this->_escaper = $escaper;
}

/**
 * Post user question
 *
 * @return void
 * @throws Exception
 */
public function execute()
{
    $post = $this->getRequest()->getParams();
    if (!$post) {
        $this->_redirect('*/*/');
        return;
    }

    $this->inlineTranslation->suspend();

    try {
        $postObject = new MagentoFrameworkDataObject();
        $postObject->setData($post);

        $error = false;

        $sender = [
            'name' => $this->_escaper->escapeHtml($post['name']),
            'email' => $this->_escaper->escapeHtml($post['email']),
        ];

        $storeScope = MagentoStoreModelScopeInterface::SCOPE_STORE;

        $transport = $this->_transportBuilder
            ->setTemplateIdentifier('email_section_sendmail_email_template') // this code we have mentioned in the email_templates.xml
            ->setTemplateOptions(
                [
                    'area' => MagentoFrameworkAppArea::AREA_FRONTEND, // this is using frontend area to get the template file
                    'store' => MagentoStoreModelStore::DEFAULT_STORE_ID,
                ]
            )
            ->setTemplateVars(['data' => $postObject])
            ->setFrom($sender)
            ->addTo($this->scopeConfig->getValue(self::XML_PATH_EMAIL_RECIPIENT, $storeScope))
            ->getTransport();


        $transport->sendMessage(); ;
        $this->inlineTranslation->resume();
        $this->messageManager->addSuccess(
            __('Thanks for contacting us with your comments and questions. We'll respond to you very soon.')
        );

    } catch (Exception $e) {
        $this->inlineTranslation->resume();
        $this->messageManager->addError(
            __('We can't process your request right now. Sorry, that's all we know.'.$e->getMessage())
        );

    }

    return $this->_redirect($this->_redirect->getRefererUrl());
}

}

app/code/Myvendor/Mymodule/view/frontend/email/email_file.html

{{template config_path="design/email/header_template"}}

 <table class="message-details">
<tr>
    <td><b>{{trans "Name"}}</b></td>
    <td>{{var data.name}}</td>
</tr>
<tr>
    <td><b>{{trans "Email"}}</b></td>
    <td>{{var data.email}}</td>
</tr>
<tr>
    <td><b>{{trans "Product Name"}}</b></td>
    <td>{{var data.product_name}}</td>
</tr>
</table>
<p><b>{{trans "Message"}}</b></p>
<p>{{var data.message}}</p>

{{template config_path="design/email/footer_template"}}

app/code/Myvendor/Mymodule/view/frontend/templates/popup.phtml

<?php
 $myBlock = MagentoFrameworkAppObjectManager::getInstance()->get('MyvendorMymoduleBlockPopup');


?>



<div class="content" style="display:none" id="popup_content">
<form
    class="form enquire"
    id="enquire-form"
    action="<?= $myBlock->escapeUrl($myBlock->getFormAction()) ?>"
    method="post">
    <div class="form-group">
        <Label for="#name">Name</Label>
        <input name="name" id="name" title="Name" class="form-control input-text" type="text"/>
    </div>
    <div class="form-group">
        <Label for="#email">Email</Label>
        <input id="email" name="email" title="Email" class="form-control input-text" type="email">
    </div>
    <div class="form-group">
        <Label for="#message">Message</Label>
        <input id="message" name="message" title="Message" type="text" class="form-control input-text">
    </div>
    <div class="form-group">
        <Label for="#product_name">Product Name</Label>
        <input id="product_name" name="product_name" title="Product Name" type="text" value="<?php if ($currentProduct = $myBlock->getCurrentProduct()) { echo $currentProduct->getName();}; ?>" class="form-control input-text" readonly><br>
    </div>
    <button type="submit">Submit</button>
</form>
</div>


<div id="click-section" class="click-section">
<br>
<button type="button" class="action primary" id="click_section2">
    <span data-bind="i18n: 'Click Me'"></span>
</button>
 </div>

  <script type="text/javascript">
  require(
    [
        'jquery',
        'Magento_Ui/js/modal/modal'
    ],
    function($,modal) {
        var options = {
            type: 'popup',
            responsive: true,
            innerScroll: true,
            title: 'Popup',
            buttons: []
        };

        $( "#click_section2" ).click(function() {
            modal(options, $('#popup_content'));
            $('#popup_content').modal('openModal');
        });
    }
);

When I click submit button:

TypeError: Argument 1 passed to MagentoFrameworkMailAddressConverter::convertMany() must be of the type array, null given,