Description:
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The special constant NULL or any value which is null can be used as an array without error, warning, or notice.

PHP version:

PHP 7.2.4 (cli) (built: Mar 28 2018 04:27:01) ( ZTS MSVC15 (Visual C++ 2017) x64 )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologies


Test script:
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$foo = NULL;
var_dump($foo[0]); // will output NULL
var_dump($foo["bar"]); // will also output NULL

Expected result:
----------------
Throw at least a warning, showing that NULL was used in an invalid way.

Actual result:
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NULL is returned