Merge pull request #138 in OP/openkit-java from bugfix/ONE-44783-fix-…

…npe to release/1.4

* commit 'ff156587beb3e5128341f51d51b678c1a0e4d32c':
  Check if InputStream is null to avoid NPE

GitOrigin-RevId: c151fd4bca880c63ac77c75ec4f5bb8c7d0ff415

src/main/java/com/dynatrace/openkit/protocol/HTTPClient.java

@@ -247,7 +247,7 @@ private Response handleResponse(RequestType requestType, HttpURLConnection conne
         int responseCode = connection.getResponseCode();
 
         String response = responseCode >= 400
-            ? readResponse(connection.getErrorStream()) // error stream is closed in readResponse
+            ? null
             : readResponse(connection.getInputStream()); // input stream is closed in readResponse
 
         if (logger.isDebugEnabled()) {
@@ -399,6 +399,10 @@ int getServerID() {
     }
 
     private static String readResponse(InputStream inputStream) throws IOException {
+        if (inputStream == null) {
+            return "";
+        }
+
         StringBuilder responseBuilder = new StringBuilder();
 
         // reading HTTP response