fix: sporadic errors where the result set cache doesn't contain a key it is supposed to contain

SVN: 14610

openbis/source/java/ch/systemsx/cisd/openbis/generic/client/web/server/resultset/CachedResultSetManager.java

@@ -330,15 +330,16 @@ public final class CachedResultSetManager<K> implements IResultSetManager<K>, Se
         if (mode == ResultSetFetchMode.COMPUTE_AND_CACHE
                 || mode == ResultSetFetchMode.CLEAR_COMPUTE_AND_CACHE)
         {
-            K dataKey = resultSetKeyProvider.createKey();
-            debug("retrieving the data with a new key " + dataKey);
-            List<T> rows = dataProvider.getOriginalData();
-            return calculateResult(sessionToken, resultConfig, dataKey, rows);
+            return calculateResultSetAndSave(sessionToken, resultConfig, dataProvider);
         } else
         {
             K dataKey = cacheConfig.tryGetResultSetKey();
             GridRowModels<T> data = fetchCachedData(dataKey);
-
+            if (data == null) // Really shoudn't happen, but these cases have been observed. 
+            {
+                return calculateResultSetAndSave(sessionToken, resultConfig, dataProvider);
+            }
+            
             if (mode == ResultSetFetchMode.FETCH_FROM_CACHE)
             {
                 return filterLimitAndSort(resultConfig, data, dataKey);
@@ -353,6 +354,15 @@ public final class CachedResultSetManager<K> implements IResultSetManager<K>, Se
         }
     }
 
+    private <T> IResultSet<K, T> calculateResultSetAndSave(final String sessionToken,
+            final IResultSetConfig<K, T> resultConfig, final IOriginalDataProvider<T> dataProvider)
+    {
+        K dataKey = resultSetKeyProvider.createKey();
+        debug("retrieving the data with a new key " + dataKey);
+        List<T> rows = dataProvider.getOriginalData();
+        return calculateResult(sessionToken, resultConfig, dataKey, rows);
+    }
+
     private <T> IResultSet<K, T> calculateResult(final String sessionToken,
             final IResultSetConfig<K, T> resultConfig, K dataKey, List<T> rows)
     {