Vector currently supports a non-standard format of values returned in buildSidebar - it allows strings or array. To encourage the standard-array let's remove support for the
This relates to cleaning up the following code and removing the deprecated is_array check
// Historically some portals have been defined using HTML rather than arrays.
// Let's move away from that to a uniform definition.
if ( !is_array( $content ) ) {
$html = $content;
$content = [];
wfDeprecated(
"`content` field in portal $name must be array."
. "Previously it could be a string but this is no longer supported.",
'1.35.0'
);
} else {
$html = false;
}