spurious error regarding mixed type

[staabm]

from time to time we see errors happen

Result cache was not saved because only files were passed as analysed paths.
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  Line   SchemaHasherMysql.php
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  63     Cannot access offset 'dbsignature' on mixed.
  77     Method staabm\PHPStanDba\DbSchema\SchemaHasherMysql::hashDb() should return string but returns mixed.
  77     Property staabm\PHPStanDba\DbSchema\SchemaHasherMysql::$hash (string|null) does not accept mixed.
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