Add sanity check

Author: newtork

cloudplatform/connectivity-apache-httpclient4/src/main/java/com/sap/cloud/sdk/cloudplatform/connectivity/AbstractHttpClientCache.java

@@ -125,6 +125,10 @@ private static boolean isHealthy( final HttpClient httpClient )
         throws IllegalArgumentException,
             NullPointerException
     {
+        if( !(httpClient instanceof HttpClientWrapper) ) {
+            log.trace("Cannot verify health of HttpClient: {}", httpClient);
+            return true;
+        }
         try {
             val hc = (CloseableHttpClient) FieldUtils.readField(httpClient, "httpClient", true);
             val cm = (PoolingHttpClientConnectionManager) FieldUtils.readField(hc, "connManager", true);