It seems like BPT\tools\tools::codec(B...n), 'SguQgUvvKRLvmCyq') can also be of type array<string,string>; however, parameter $json of json_decode() does only seem to accept string, maybe add an additional type check?
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Ignorable by Annotation
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If this is a false-positive, you can also ignore this issue in your code via the ignore-type annotation