Ninja Forms Input Fields Empty After Submission With Validation Error

<?php

echo do_shortcode('[ninja_forms id=1]'); 

$tmphtml = "";

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
 
 $ninja_form_id = $_POST["_form_id"];
 
 if ( $ninja_form_data == 1 ){ // Your Form ID
 
 $tmphtml .= '<script>';
 
 foreach ($_POST as $key => $val) {
 
 if (strpos($key, 'ninja_forms_field') !== false && $val <> '' && $val <> 'unchecked') {
 
 $tmphtml .= 'document.getElementById("' . $key . '").value = "' . $val . '";';
 
 }
 
 }
 
 $tmphtml .= '</script>';
 
 }
 
 echo $tmphtml;
}