在PHP中将JSON字符串转换为关联数组

What I'm trying to Do is so simple yet everything I tries had failed. I have the following string: "{"msg":"background1.jpg"}", and I want to convert it to an array to access the msg value. this should simply be done like so(or so I've thought):

$theString = "{"msg":"background1.jpg"}";

var_dump(json_decode($theString, TRUE));

The vr_dump() is dumping NULL, also tried:

var_dump(json_decode(json_encode($theString), TRUE));

This dumps string(45) "{"msg":"background1.jpg"}"

and tried many many more things, but all failed. Any thought please.

EDIT:

I'm getting the json string from database, where i have previously stored like so:

$toBeStored = json_encode(array("msg" => $value));

Try this

$var = '{"msg": "background1.jpg"}';

var_dump($var);

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