Description:
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If a key in an array starts with the null byte, json_encode ignores that key=>value pair.

This seems wrong because json_encode doesn't care about null bytes anywhere in the value (and neither does javascript, about keys or values).

Reproduce code:
---------------
//works as expected:
echo json_encode(array(0,"a\0b"=>1,"\0null-prefixed value"));

echo "\n\n";

//ignores second element whose key begins with null byte:
echo json_encode(array(0,"\0ab"=>1,"\0null-prefixed value"));

Expected result:
----------------
{"0":0,"a\0b":1,"1":"\0null-prefixed value"}

{"0":0,"\0ab":1,"1":"\0null-prefixed value"}




// \0 represents an actual null byte here

Actual result:
--------------
{"0":0,"a\0b":1,"1":"\0null-prefixed value"}

{"0":0,"1":"\0null-prefixed value"}




// \0 represents an actual null byte here