Use '===' operator to check if file was written.

This prevents incorrect logic when writing empty string (0 bytes).

Author: vovayatsyuk

lib/internal/Magento/Framework/Filesystem/Driver/File.php

@@ -552,7 +552,7 @@ public function touch($path, $modificationTime = null)
     public function filePutContents($path, $content, $mode = null)
     {
         $result = @file_put_contents($this->getScheme() . $path, $content, $mode);
-        if (!$result) {
+        if ($result === false) {
             throw new FileSystemException(
                 new \Magento\Framework\Phrase(
                     'The specified "%1" file couldn\'t be written. %2',

lib/internal/Magento/Framework/Filesystem/Driver/Http.php

@@ -109,7 +109,7 @@ public function fileGetContents($path, $flags = null, $context = null)
     public function filePutContents($path, $content, $mode = null, $context = null)
     {
         $result = @file_put_contents($this->getScheme() . $path, $content, $mode, $context);
-        if (!$result) {
+        if ($result === false) {
             throw new FileSystemException(
                 new \Magento\Framework\Phrase(
                     'The specified "%1" file couldn\'t be written. %2',

lib/internal/Magento/Framework/Filesystem/Io/File.php

@@ -479,7 +479,7 @@ public function write($filename, $src, $mode = null)
         } else {
             $result = @file_put_contents($filename, $src);
         }
-        if ($mode !== null && $result) {
+        if ($mode !== null && $result !== false) {
             @chmod($filename, $mode);
         }
         $this->_iwd();