Fix addcslashes(), strpos(): Passing null to parameter #1 ($string) of type string is deprecated (#616)

Summary:
`Deprecated: addcslashes(): Passing null to parameter #1 ($string) of type string is deprecated {"exception":"[object] (ErrorException(code: 0): Deprecated: addcslashes(): Passing null to parameter #1 ($string) of type string is deprecated at /app/vendor/facebook/php-business-sdk/src/FacebookAds/Logger/CurlLogger.php:160)"} []

Deprecated: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated {"exception":"[object] (ErrorException(code: 0): Deprecated: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated at /app/vendor/facebook/php-business-sdk/src/FacebookAds/Logger/CurlLogger.php:161)"} []`

Pull Request resolved: #616

Reviewed By: liliarizona

Differential Revision: D67467808

Pulled By: stcheng

fbshipit-source-id: 39b7f5e24b5b0314fcbaa271169c5c23b3b2afe0

Author: mbvb1223

src/FacebookAds/Logger/CurlLogger.php

@@ -157,6 +157,7 @@ protected function processParams(Parameters $params, $method, $is_file) {
       if ($is_file && $params->offsetGet($name) instanceof FileParameter) {
         $value = "@" . $this->normalizeFileParam($params->offsetGet($name));
       } else {
+        $value = (string) $value;
         $value = addcslashes(
           strpos($value, "\n") !== false
             ? $this->indent($value, 2)