fix nullpointerexception on calculate average values of collection report

Author: coy123

curation-module-core/src/main/java/eu/clarin/cmdi/curation/report/CollectionReport.java

@@ -363,8 +363,11 @@ public void calculateAverageValues() {
                                     Accumulators.max("max_resp", "$duration")
                             )));
             Document result = aggregate.first();
-            urlReport.avgRespTime = result.getDouble("avg_resp");
-            urlReport.maxRespTime = result.getLong("max_resp");
+
+            if(result!=null){
+                urlReport.avgRespTime = result.getDouble("avg_resp");
+                urlReport.maxRespTime = result.getLong("max_resp");
+            }
 
         }
 
@@ -463,8 +466,6 @@ public static class URLValidationReport {
         public int totNumOfUniqueLinks;
         public int totNumOfCheckedLinks;
         public Double avgNumOfUniqueLinks = 0.0;
-        //        public int totNumOfResProxiesLinks;
-//        public Double avgNumOfResProxiesLinks = 0.0;
         public int totNumOfBrokenLinks;
         public Double avgNumOfBrokenLinks = 0.0;
         public Double ratioOfValidLinks = 0.0;