How to differentiate a value is zero or null in php?

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I have a variable e.g $moon

In some cases its value is

$moon=0;

In other cases its value is

$moon=NULL;

Now in if clause how can i differentiate between these values?

My code is

if($moon==0 && !empty($moon)){
    echo "its zero";
}else{
    echo "its null";
}

it always shows "its zero"

I also tried

if($moon==0 && $moon!=NULL){
    echo "its zero";
}else{
    echo "its null";
}


to check for null use :

if (is_null($moon))

to check for integer 0 use:

if ($moon === 0)

to check for integer 0 or string "0"

if ($moon == '0')

I have to add that php will consider any string equals with number 0 when using "==":

$moon = "asd";

if ($moon == 0) // will be true