fixed a bug if a certificate was generally not trusted but the causes were deemed null

Author: ic0ns

src/main/java/de/rub/nds/tlsscanner/probe/certificate/CertificateChain.java

@@ -201,9 +201,11 @@ public CertificateChain(Certificate certificate, String uri) {
             CertPathValidationResult certPathValidationResult = evaluateGeneralTrust(orderedCertificateChain);
             generallyTrusted = certPathValidationResult.isValid();
             if (!generallyTrusted) {
-                CertPathValidationException[] causes = certPathValidationResult.getCauses();
-                for (CertPathValidationException exception : causes) {
-                    exception.printStackTrace();
+                if (certPathValidationResult.getCauses() != null) {
+                    CertPathValidationException[] causes = certPathValidationResult.getCauses();
+                    for (CertPathValidationException exception : causes) {
+                        exception.printStackTrace();
+                    }
                 }
             }
         } else {