I have a couple of dropdown's that I'm using to filter the results for a custom query.
This is part of the code I use for filter the results.
// tax query 'tax_query' => array( 'relation' => 'AND', array( 'taxonomy' => 'zonas', 'field' => 'slug', 'terms' => $zona, 'operator' => 'IN' ) )
If an item of the dropDown "zona" was selected, that's the value I use for the $zona variable.
What should be the value of $zona, if I don't want to filter by that term? (when nothing is selected from the "zona" dropdown)
I tried with "NULL", but that doesn't work.