Description:
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I found out that current PHP does not emit warnings at least for the following expressions:

a) if boolean is accessed with index:
  false['x']

b) if null is accessed with index:
  null['x']

in contrary with string type, which emits the following message:
Warning: Illegal string offset 'x'...
Notice: Uninitialized string offset: 0

I would expect PHP to emit at least Notice warning.

Is this a bug which needs to be addressed or is this an intended behaviour for some use case/backcompatibility that requires no warning?

Test script:
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see desc.