Fix a rare edge-case bug where invalid values in tax_query terms resulted in a broken query

[rinatkhaziev]

Description of the Change

Having a tax_query with terms being an array of not valid values results in a broken query.

{
	"tax_query": [
		{
				"taxonomy": "category",
				"field": "slug",
				"terms": [
						null
				],
				"operator": "IN"
		},
		{
				"taxonomy": "category",
				"field": "term_id",
				"terms": [
						1
				],
				"operator": "NOT IN"
		}
	]
}

=> 400

{
        "error": {
            "root_cause": [
                {
                    "type": "parsing_exception",
                    "reason": "No value specified for terms query",
                    "line": 1,
                    "col": 507
                }
            ],
            "type": "parsing_exception",
            "reason": "No value specified for terms query",
            "line": 1,
            "col": 507
        }

Alternate Designs

Not sure, this seemed like a most logical place to put it to ensure no invalid terms would ever make it into the final query.

Possible Drawbacks

This is still not 100% bulletproof because in even edgier case where a non-empty array or an object instance is passed it would not get filtered by array_filter. E.g. this would likely break the query.

'terms' => [ [ 'arr' ], new YouShouldNotDoThat() ];

Verification Process

	// Without the fix
	$q = new WP_Query( [
		'ep_integrate' => true,
		'tax_query' => [
			array(
            'taxonomy' => 'category',
            'field'    => 'slug',
            'terms'    => [ null ],
        ),
		]
	] );

	var_dump( $q->elasticsearch_success ); // => false
	// With the fix
	$q = new WP_Query( [
		'ep_integrate' => true,
		'tax_query' => [
			array(
            'taxonomy' => 'category',
            'field'    => 'slug',
            'terms'    => [ null ],
        ),
		]
	] );

	var_dump( $q->elasticsearch_success ); // => true

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

Fixed - Invalid values in tax_query terms won't result in a query failure

Credits

Props @rinatkhaziev