add nullcheck in scanDirectory() on result of scanFile()

dependency-check-core/src/main/java/org/owasp/dependencycheck/Engine.java

@@ -552,7 +552,9 @@ public class Engine implements FileFilter, AutoCloseable {
                     }
                 } else {
                     final Dependency d = scanFile(f, projectReference);
-                    deps.add(d);
+                    if(d != null){
+						deps.add(d);
+					}
                 }
             }
         }