Description:
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When calling is_null(1) for a varibale and compare it with 
null I get different result. 
Shouldn't it produce the same result? 

Reproduce code:
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$arr = array();

echo( is_null( $arr ) ? "is_null: NULL\n" : "is_null: NOT NULL\n" );

echo( (null == $arr) ? "null: NULL\n" : "null: NOT NULL\n" );

Expected result:
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is_not: NOT NULL 
null: NULL