What's the difference between is_null($var) and ($var === null)?

Is there any difference between this...

if (is_null($var)) {
    do_something();
}

and this?

if ($var === null) {
    do_something();
}

Which form is better when checking whether or not a variable contains null? Are there any edge cases I should be aware of? (I initialize all my variables, so nonexistent variables are not a problem.)

empty() and isset() do not trigger a PHP warning if their parameter is an undefined variable. In most cases, such a warning is desirable to pinpoint the bugs. So only use the functions if you believe your variable can be legitimately undefined. It normally happens with an array index.

✅ is true

❌ is false

        |  isset   | is_null | === null | == null | empty   |
|-------|----------|---------|----------|---------|---------|
| unset |    ❌   |    ✅   |    ✅    |    ✅  |    ✅   |
|  null |    ❌   |    ✅   |    ✅    |    ✅  |    ✅   |
|  true |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
| false |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|     0 |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|     1 |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
|    \0 |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
|    "" |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|    [] |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |

Summary: