fix(2meet-data-optimizer): compare empty strings correctly when retiring a group

- retire() read native meta with wpdb::get_col(), which (via get_var())
  returns null for an empty string, so a flat '' written back as '' was
  counted as a mismatch and blocked the retirement. It now reads raw rows
  with get_results().
- The integration test wpdb stub's get_var() / get_col() now read '' as
  null like the real wpdb, so tests see WordPress behaviour.
- Found writing back the sso group on dev21 / dev22 (picture_url = '').
- Verify: core unit 658 / integration 480 green, phpcs clean
- PR: PR-042 follow-up

includes/migration/class-tmdo-native-restorer.php

@@ -168,8 +168,9 @@ final class TMDO_Native_Restorer {
 				if ( '' === $col || ! isset( $row[ $col ] ) ) {
 					continue;
 				}
-				$want   = (string) maybe_serialize( TMDO_Type_Caster::from_db( $row[ $col ], $field ) );
-				$native = $wpdb->get_col( $wpdb->prepare( "SELECT meta_value FROM `{$native_table}` WHERE `{$id_col}` = %d AND meta_key = %s", (int) $row[ $id_col ], $field['key'] ) );
+				$want = (string) maybe_serialize( TMDO_Type_Caster::from_db( $row[ $col ], $field ) );
+				// get_results(), not get_col(): wpdb reads an empty string as null.
+				$native = array_column( (array) $wpdb->get_results( $wpdb->prepare( "SELECT meta_value FROM `{$native_table}` WHERE `{$id_col}` = %d AND meta_key = %s", (int) $row[ $id_col ], $field['key'] ), ARRAY_A ), 'meta_value' );
 				if ( array( $want ) !== $native ) {
 					++$result['mismatches'];
 				}

tests/integration/NativeRestorerRetireTest.php

@@ -129,6 +129,15 @@ class NativeRestorerRetireTest extends TestCase {
 		$this->assertSame( 3, $result['mismatches'], 't1, ["1.1.1.1"], t2 are not native yet' );
 	}
 
+	public function test_empty_string_values_count_as_written_back(): void {
+		global $wpdb;
+		$wpdb->query( 'UPDATE `' . self::A . "` SET ips = '' WHERE user_id = 2" );
+		TMDO_Native_Restorer::run( 'user', false, 500, false, 'rt_a' );
+		self::register( false );
+
+		$this->assertSame( 'retired', TMDO_Native_Restorer::retire( 'user', 'rt_a' )['status'], "wpdb::get_col() reads '' as null" );
+	}
+
 	public function test_retire_forgets_the_group_and_keeps_its_table_as_a_backup(): void {
 		global $wpdb;
 		TMDO_Native_Restorer::run( 'user', false, 500, false, 'rt_a' );

tests/integration/bootstrap.php

@@ -129,7 +129,8 @@ $wpdb = new class( $_mysqli ) {
 	public function get_var( string $sql ): ?string {
 		$result = $this->db->query( $sql );
 		if ( ! $result || ! ( $row = $result->fetch_row() ) ) { return null; }
-		return $row[0] !== null ? (string) $row[0] : null;
+		// Like wpdb::get_var(): an empty string reads as null.
+		return null !== $row[0] && '' !== $row[0] ? (string) $row[0] : null;
 	}
 
 	public function get_row( string $sql, $output = 'OBJECT' ) {
@@ -152,7 +153,8 @@ $wpdb = new class( $_mysqli ) {
 		$result = $this->db->query( $sql );
 		if ( ! $result ) { return []; }
 		$values = [];
-		while ( $row = $result->fetch_row() ) { $values[] = $row[ $col_index ] ?? null; }
+		// Like wpdb::get_col() (per-row get_var()): an empty string reads as null.
+		while ( $row = $result->fetch_row() ) { $values[] = isset( $row[ $col_index ] ) && '' !== $row[ $col_index ] ? $row[ $col_index ] : null; }
 		return $values;
 	}