Check if variable is true, false, set null if nothing - php

Question

i am struggling with a rather simple task.
I am working with a REST backend, which sometimes receive a json-object as parameter like "api?params={"foo":bar}" . And "foo" can be true/false or null (undefined).
When i echo myParam(foo) when true, it echoes "true".
When foo is false, it returns nothing (i'd like it to echo "false"),
but when foo is not defined, when its not in the API-call, i want it to return "null".
I found a snippet on the net a long time a go, which i thought was working.
$foo = (null !== $jsonObj->foo ? $jsonObj->foo: "");
But its not working when foo is false or null.
$foo = var_export($jsonObj->foo, true);
This line however returns the variable as string, and returns it "correct", it returns "true" when true, "false" when false and "NULL" when null. And this i can work with .
switch ($foo) {
case "true":
$result = true;
break;
...
But, there must be a better way ? Right?
--- UPDATE ---
The solution that worked for me now was this:
(since im storing the value in an array, storing false will equal "")
$foo = is_null($jsonObj->foo) ? null : $jsonObj->foo;
This gave me foo = null if null/undefined, else true/false...
Then to store it in array, i used this:
$array["foo"] = (!is_null($foo) ? intval($foo) : null);
this stored it as 0/1 or "" if it was null, then i have 3 states i can work with.
But reading all your comments made me try for the best of solutions.

Answer 1

You could use php isset() function.
i.e. :
if (!isset($foo)) {
echo "foo is not set : ";
var_dump($foo);
echo "<br />";
}
// returns "foo is not set : NULL"
$foo = NULL;
if (!isset($foo)) {
echo "foo = NULL : ";
var_dump($foo);
echo "<br />";
}
// returns "foo = NULL : NULL"
$foo = false;
if (isset($foo)) {
echo "foo = false : ";
var_dump($foo);
echo "<br />";
}
// returns "foo = false : bool(false)"
$foo = true;
if (isset($foo)) {
echo "foo = true : ";
var_dump($foo);
}
// returns "foo = true : bool(true)"
Hope it helps.

Answer 2

I guess you are mixing up a string that contains "true" with a real boolean "true".
Use var_dump always to ensure the correct type of variables too.
var_dump($jsonObj->foo)
This will show you the exact type.
So if it is a string you have to check with something like (what you already to in the switch)
if($jsonObj->foo == "true")