Avoid is_null

Author: GrahamCampbell

src/Loader.php

@@ -252,7 +252,7 @@ protected function resolveNestedVariables($value)
                 '/\${([a-zA-Z0-9_]+)}/',
                 function ($matchedPatterns) use ($loader) {
                     $nestedVariable = $loader->getEnvironmentVariable($matchedPatterns[1]);
-                    if (is_null($nestedVariable)) {
+                    if ($nestedVariable === null) {
                         return $matchedPatterns[0];
                     } else {
                         return $nestedVariable;
@@ -333,7 +333,7 @@ public function setEnvironmentVariable($name, $value = null)
 
         // Don't overwrite existing environment variables if we're immutable
         // Ruby's dotenv does this with `ENV[key] ||= value`.
-        if ($this->immutable === true && !is_null($this->getEnvironmentVariable($name))) {
+        if ($this->immutable === true && $this->getEnvironmentVariable($name) !== null) {
             return;
         }
 

src/Validator.php

@@ -41,7 +41,7 @@ public function __construct(array $variables, Loader $loader)
 
         $this->assertCallback(
             function ($value) {
-                return !is_null($value);
+                return $value !== null;
             },
             'is missing'
         );