public function server($key = null, $default = null, $nullIfEmpty = false) {
        return InternalHelper::getSingleKeyOrAll($this->serverVariables, $key, $default, $nullIfEmpty);
    }
public function server($key = null, $default = null, $nullIfEmpty = false) {
        return InternalHelper::getSingleKeyOrAll($this->serverVariables, $key, $default, $nullIfEmpty);
    }
public function server ( $ key = null , $ default = null , $ nullIfEmpty = false ) { return InternalHelper :: getSingleKeyOrAll ( $ this -> serverVariables , $ key , $ default , $ nullIfEmpty ) ; }
Returns server variables.

@param string|null $key The key to get. Default: null - all variables.
@param string|null $default The default value if the key is not null, and the value with the specified key was not found. The default value is null.
@param bool $nullIfEmpty Check the value with the empty() function. If empty() returns true, the function returns $default.

@return array|string
Returns server variables .