getMigrationLastImportedTime must return string

[martin-klima]

Method getMigrationLastImportedTime must return a string, but returns FALSE for migrations that have never run.

Migrations that have never run, have FALSE b:0; in the key_value table.

$this->keyValue->get($migration->id(), '') returns FALSE.

drush/src/Commands/core/MigrateRunnerCommands.php

Line 282 in 6004108

return $lastImported;

It causes an error:

TypeError: Drush\Commands\core\MigrateRunnerCommands::getMigrationLastImportedTime(): Return value must be of type string, bool returned in Drush\Commands\core\MigrateRunnerCommands->getMigrationLastImportedTime() (line 282 of /var/www/vendor/drush/drush/src/Commands/core/MigrateRunnerCommands.php).

Possible solution:
Use
return (string) $lastImported;

instead of
return $lastImported;

It will convert FALSE to the empty character.