( ! ) Warning: in_array() expects parameter 2 to be array, boolean given in

[amgolden]

I just installed the wA11y plugin on a test WordPress 4.9.8 instance running locally on WampServer. I'd love to test this plugin but I'm getting the following error.

Line 414 in my editor is:
if ( ! in_array( 'wave', $enabled_tools ) ) {

The copied and pasted error table:
( ! ) Warning: in_array() expects parameter 2 to be array, boolean given in C:\wamp64\www\wp\wp-content\plugins\wa11y\wa11y.php on line 414
Call Stack

Time Memory Function Location

1 0.0005 323448 {main}( ) ...\post.php:0
2 0.3655 40710872 include( 'C:\wamp64\www\wp\wp-admin\edit-form-advanced.php' ) ...\post.php:174
3 0.3872 41406624 do_action( ) ...\edit-form-advanced.php:334
4 0.3872 41407312 WP_Hook->do_action( ) ...\plugin.php:453
5 0.3872 41407392 WP_Hook->apply_filters( ) ...\class-wp-hook.php:310
6 0.3872 41408192 call_user_func_array:{C:\wamp64\www\wp\wp-includes\class-wp-hook.php:286} ( ) ...\class-wp-hook.php:286
7 0.3872 41408688 Wa11y_Admin->add_post_meta_boxes( ) ...\class-wp-hook.php:286
8 0.3873 41408856 Wa11y->can_load_wave( ) ...\admin.php:172
9 0.3879 41389040 in_array ( ) ...\wa11y.php:414