fix: blank snippets page when another plugin's screen_settings filter returns null

src/php/Admin/Menus/Manage/Manage_Menu_Screen_Options.php

@@ -147,11 +147,21 @@ public function is_upsell_view(): bool {
 	/**
 	 * Render the manage table controls.
 	 *
-	 * @param string $screen_settings Existing screen settings HTML.
+	 * Anything may filter `screen_settings` before this runs, and a callback
+	 * that forgets to return its value hands the next one null. Declaring the
+	 * parameter as a string turned that into a fatal error, and because it is
+	 * raised while the screen meta is being rendered, the page dies after the
+	 * admin chrome but before any content: the snippets screen appears blank
+	 * while the rest of the admin looks fine.
+	 *
+	 * @param mixed $screen_settings Existing screen settings HTML, from an
+	 *                               unknown number of earlier callbacks.
 	 *
 	 * @return string
 	 */
-	public function render( string $screen_settings ): string {
+	public function render( $screen_settings ): string {
+		$screen_settings = is_string( $screen_settings ) ? $screen_settings : '';
+
 		if ( $this->is_cloud_community_view() ) {
 			return $screen_settings;
 		}

tests/unit/Admin/Menus/Manage/Manage_Menu_Screen_Options_Test.php

@@ -74,6 +74,41 @@ public function test_render_skips_truncation_toggle_on_cloud_community_view(): v
 		$this->assertFalse( $options->is_manage_table_view() );
 	}
 
+	/**
+	 * An earlier `screen_settings` callback that returns null must not be fatal.
+	 *
+	 * A callback that forgets to return its value passes null down the chain.
+	 * That used to raise a TypeError while the screen meta was rendering, which
+	 * killed the page after the admin chrome but before the snippets table.
+	 *
+	 * @return void
+	 */
+	public function test_render_tolerates_a_null_value_from_an_earlier_callback(): void {
+		$options = new Manage_Menu_Screen_Options();
+
+		$output = $options->render( null );
+
+		$this->assertIsString( $output );
+		$this->assertStringContainsString( 'snippets-table-truncate-row-values', $output );
+	}
+
+	/**
+	 * The filter chain survives a callback that returns null.
+	 *
+	 * @return void
+	 */
+	public function test_screen_settings_filter_chain_survives_a_null_returning_callback(): void {
+		$options = new Manage_Menu_Screen_Options();
+		$options->load();
+
+		add_filter( 'screen_settings', '__return_null', 5 );
+		$output = apply_filters( 'screen_settings', '', get_current_screen() );
+		remove_filter( 'screen_settings', '__return_null', 5 );
+
+		$this->assertIsString( $output );
+		$this->assertStringContainsString( 'snippets-table-truncate-row-values', $output );
+	}
+
 	/**
 	 * The truncation preference is saved from the Screen Options form.
 	 *