SDAP-201 Empty CSV data results with NullPointerException. (#49)

diff --git a/core/src/main/java/org/apache/sdap/mudrod/ssearch/ranking/DataGenerator.java b/core/src/main/java/org/apache/sdap/mudrod/ssearch/ranking/DataGenerator.java
index f6153bc..3c0763a 100644
--- a/core/src/main/java/org/apache/sdap/mudrod/ssearch/ranking/DataGenerator.java
+++ b/core/src/main/java/org/apache/sdap/mudrod/ssearch/ranking/DataGenerator.java
@@ -108,6 +108,9 @@
               calculateVec(dataArr);
             }
           }
+          if (dataArr == null) {
+            throw new RuntimeException("Specified CSV file content is empty to create header data!");
+          }
           storeHead(dataArr); // Store the header
         }
       } else // Process only one file