lumen illuminate/validation validator goes wrong with integer rule

I recently met an issue with validator (illuminate/validation) under Lumen (5.4.6) (Laravel Components 5.4.*). It seems like the integer rule doesn't work.

I used Paw(or postman) to send companyName with type string and it can pass the validation and 'here i am' can printed out. Even a boolean type, let's say (boolean)companyName=TRUE can pass the validation. Have you met the same issue? this bug is quite obvious but I didn't find the similar discussion on google.

I also tested the string rule 'required|string|min:1' and it works accordingly, neither integer nor boolean parameters can pass the validation.

code screen-shot

via Chebli Mohamed