API will create PHP warning and thus break code on empty category

[apermo]

Example Request

array (size=3)
  'headers' => 
    array (size=)
      'Authorization' => string 'Basic randomstring==' (length=34)
  'body' => 
    array (size=15)
      'title' => string 'Test' (length=4)
      'status' => string 'publish' (length=7)
      'content' => string '' (length=0)
      'date' => string '2018-06-04 17:11:32' (length=19)
      'date_gmt' => string '2018-06-04 15:11:32' (length=19)
      'modified' => string '2018-06-05 10:24:01' (length=19)
      'modified_gmt' => string '2018-06-05 08:24:01' (length=19)
      'excerpt' => string '' (length=0)
      'slug' => string 'test' (length=4)
      'type' => string 'post' (length=4)
      'comment_status' => string 'closed' (length=6)
      'ping_status' => string 'closed' (length=6)
      'sticky' => boolean false
      'categories' => string '' (length=0)
      'tags' => string '' (length=0)
  'method' => string 'POST' (length=4)

This will lead to warnings when Debug is active on the remote node.

Warning: Invalid argument supplied for foreach() in /path/to/public_html/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php on line 1256

I suggest to replace (1251-1253):

<?php
if ( ! isset( $request[ $base ] ) ) {
        continue;
}

With:

<?php
if ( ! isset( $request[ $base ] ) || ! is_array( $request[ $base ] ) ) {
        continue;
}

This will avoid entering the loop and the warning

[swissspidy]

We could also use is_iterable() now, see #43619.

[apermo]

Fine for me too ;) As long as it avoids throwing a warning.

[skostadinov]

Added is_iterable() check for the handle_terms() and check_assign_terms_permission()