[ClassLoader] Fix storing not-found classes in APC cache

ApcClassLoader.php

@@ -122,8 +122,10 @@ class ApcClassLoader
      */
     public function findFile($class)
     {
-        if (false === $file = apcu_fetch($this->prefix.$class)) {
-            apcu_store($this->prefix.$class, $file = $this->decorated->findFile($class));
+        $file = apcu_fetch($this->prefix.$class, $success);
+
+        if (!$success) {
+            apcu_store($this->prefix.$class, $file = $this->decorated->findFile($class) ?: null);
         }
 
         return $file;

ApcUniversalClassLoader.php

@@ -87,8 +87,10 @@ class ApcUniversalClassLoader extends UniversalClassLoader
      */
     public function findFile($class)
     {
-        if (false === $file = apcu_fetch($this->prefix.$class)) {
-            apcu_store($this->prefix.$class, $file = parent::findFile($class));
+        $file = apcu_fetch($this->prefix.$class, $success);
+
+        if (!$success) {
+            apcu_store($this->prefix.$class, $file = parent::findFile($class) ?: null);
         }
 
         return $file;

DebugClassLoader.php

@@ -74,7 +74,7 @@ class DebugClassLoader
      */
     public function findFile($class)
     {
-        return $this->classFinder->findFile($class);
+        return $this->classFinder->findFile($class) ?: null;
     }
 
     /**

WinCacheClassLoader.php

@@ -123,8 +123,10 @@ class WinCacheClassLoader
      */
     public function findFile($class)
     {
-        if (false === $file = wincache_ucache_get($this->prefix.$class)) {
-            wincache_ucache_set($this->prefix.$class, $file = $this->decorated->findFile($class), 0);
+        $file = wincache_ucache_get($this->prefix.$class, $success);
+
+        if (!$success) {
+            wincache_ucache_set($this->prefix.$class, $file = $this->decorated->findFile($class) ?: null, 0);
         }
 
         return $file;

XcacheClassLoader.php

@@ -126,7 +126,7 @@ class XcacheClassLoader
         if (xcache_isset($this->prefix.$class)) {
             $file = xcache_get($this->prefix.$class);
         } else {
-            $file = $this->decorated->findFile($class);
+            $file = $this->decorated->findFile($class) ?: null;
             xcache_set($this->prefix.$class, $file);
         }