PHP Error[2]: openssl_encrypt(): Using an empty Initialization Vector (iv) is potentially insecure and not recommended

/**
 * Encrypts data
 * @link http://php.net/manual/en/function.openssl-encrypt.php
 * @param string $data <p>
 * The data.
 * </p>
 * @param string $method <p>
 * The cipher method.
 * </p>
 * @param string $key <p>
 * The key. For a list of available cipher methods, use {@see openssl_get_cipher_methods()}.
 * </p>
 * @param int $options [optional] <p>
 * options is a bitwise disjunction of the flags OPENSSL_RAW_DATA and OPENSSL_ZERO_PADDING.
 * </p>
 * @param string $iv [optional] <p>
 * A non-NULL Initialization Vector.
 * </p>
 * @param string &$tag <p>The authentication tag passed by reference when using AEAD cipher mode (GCM or CCM).</p>
 * @param string $aad <p>Additional authentication data.</p>
 * @param int $tag_length [optional] <p>
 * The length of the authentication tag. Its value can be between 4 and 16 for GCM mode.
 * </p>
 * @return string the encrypted string on success or false on failure.
 * @since 5.3.0
 */
function openssl_encrypt($data, $method, $key, $options = 0, $iv = "", &$tag = NULL, $aad = "", $tag_length = 16) { }