PHPCS 4.0: handle converting empty string array values to null

PHPCS 4.0 introduced a change where empty string values in array
properties are converted to `null`. This is documented in the
Version 4.0 Developer Upgrade Guide (https://github.com/PHPCSStandards/PHP_CodeSniffer/wiki/Version-4.0-Developer-Upgrade-Guide#property-type-casting-has-been-made-more-consistent):

> Array elements can now no longer contain an empty string value
> as that value will be cast to `null`.

This affected the sniffs PrefixAllGlobals and NoSilencedErrors.
Both pass array values to `strtolower()`, which triggers a PHP 8.5
deprecation warning when `null` is passed.

The fix is different for each sniff:

- PrefixAllGlobals: Convert `null` back to empty string at the
start of the validation loop. This preserves the "prefix too short"
error that alerts users about invalid configuration.

- NoSilencedErrors: Filter out `null` values before processing.
Unlike PrefixAllGlobals, this sniff has no validation that
provides user feedback for invalid entries, so filtering is cleaner.
A test case was added to safeguard against the deprecation.

Author: rodrigoprimo

WordPress/Sniffs/NamingConventions/PrefixAllGlobalsSniff.php

@@ -1229,6 +1229,9 @@ private function validate_prefixes() {
 		$prefixes    = array();
 		$ns_prefixes = array();
 		foreach ( $this->prefixes as $key => $prefix ) {
+			// PHPCS >= 4.0 converts empty string values in array properties to null.
+			// Convert null back to empty string to preserve the "prefix too short" error.
+			$prefix   = $prefix ?? '';
 			$prefixLC = strtolower( $prefix );
 
 			if ( isset( $this->prefix_blocklist[ $prefixLC ] ) ) {

WordPress/Sniffs/PHP/NoSilencedErrorsSniff.php

@@ -186,6 +186,9 @@ public function register() {
 	public function process_token( $stackPtr ) {
 		// Handle the user-defined custom function list.
 		$this->customAllowedFunctionsList = RulesetPropertyHelper::merge_custom_array( $this->customAllowedFunctionsList, array(), false );
+		// PHPCS >= 4.0 converts empty string values in array properties to null.
+		// Filter out null values to avoid passing them to strtolower().
+		$this->customAllowedFunctionsList = array_filter( $this->customAllowedFunctionsList );
 		$this->customAllowedFunctionsList = array_map( 'strtolower', $this->customAllowedFunctionsList );
 
 		/*

WordPress/Tests/PHP/NoSilencedErrorsUnitTest.inc

@@ -92,3 +92,11 @@ $file = @MyNS\MyClass::file_get_contents( $file ); // Bad.
 $file = @MyNS\MyClass\file_exists( $file ); // Bad.
 $file = @namespace\MyNS\MyClass::file( $file ); // Bad.
 $file = @namespace\is_dir( $dir ); // The sniff should stop flagging this once it can resolve relative namespaces.
+
+/*
+ * Safeguard handling of empty prefix values (PHPCS 4.x compatibility).
+ * PHPCS >= 4.0 converts empty string values in array properties to null.
+ */
+// phpcs:set WordPress.PHP.NoSilencedErrors customAllowedFunctionsList[] ,
+$unserialized = @unserialize( $str );
+// phpcs:set WordPress.PHP.NoSilencedErrors customAllowedFunctionsList[]