PHP Loose comparison and null on Switch - php

Question

Today I saw a strange bug on my code.
I have a switch with comparison on case and if my variable equals null or '' it will always comes in the first case.
My code :
$sHost = filter_input(INPUT_SERVER, 'HTTP_HOST');
switch($sHost){
// Local
case strpos($sHost, "dev.localhost") !== false: $this->_sEnv = 'local';
break;
// Prod
default: $this->_sEnv = 'production';
break;
}
On an if statement it's work but on switch case it doesn't work , I don't know why .. Maybe a PHP problems ? Anyone has had a similar bug ?
$sHost can be null because sometimes I run the script with a batch.
if(strpos($sHost, "dev.localhost") !== false){
// Nothing
}
else{
return false;
}
Of course I can do an if is_null before the switch , but I want to understand why it's working like that..
Edit: I forgot to said I have 5 cases on my switch , one case by environment
Thank you for your future answer :)

Answer 1

If $sHost equals to null or '', then the first switch case is always true because
var_dump($sHost == (strpos($sHost, "dev.localhost") !== false));
is true. How switch work.
You can do this:
switch(true) {
// Local
case strpos($sHost, "dev.localhost") !== false:
$this->_sEnv = 'local';
break;
// Prod
default:
$this->_sEnv = 'production';
break;
}

Answer 2

switch(strpos($sHost, "dev.localhost")){
// Local
case -1: $this->_sEnv = 'production';
break;
// Prod
default: $this->_sEnv = 'local';
break;
}
#Leggendario, good point, fixed above.