Fix bug in classed group queries

Change-Id: Ie7713203ecca31ce06d535054608fca3c4d445e5
diff --git a/src/main/java/de/ids_mannheim/korap/query/spans/ElementDistanceExclusionSpans.java b/src/main/java/de/ids_mannheim/korap/query/spans/ElementDistanceExclusionSpans.java
index 1c5ebdc..a5adc05 100644
--- a/src/main/java/de/ids_mannheim/korap/query/spans/ElementDistanceExclusionSpans.java
+++ b/src/main/java/de/ids_mannheim/korap/query/spans/ElementDistanceExclusionSpans.java
@@ -10,8 +10,10 @@
 import org.apache.lucene.index.Term;
 import org.apache.lucene.index.TermContext;
 import org.apache.lucene.search.spans.Spans;
+import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.util.Bits;
 
+
 import de.ids_mannheim.korap.query.SpanDistanceQuery;
 
 /**
@@ -68,7 +70,7 @@
                                           Map<Term, TermContext> termContexts)
             throws IOException {
         super(query, context, acceptDocs, termContexts);
-
+        
         elements = query.getElementQuery().getSpans(context, acceptDocs,
                 termContexts);
         hasMoreElements = elements.next();
@@ -79,7 +81,11 @@
         this.isOrdered = query.isOrdered();
         candidateList = new ArrayList<CandidateSpan>();
         targetList = new ArrayList<CandidateSpan>();
-        currentDocNum = firstSpans.doc();
+        
+        if (hasMoreSpans)
+            currentDocNum = firstSpans.doc();
+        else
+            currentDocNum = DocIdSetIterator.NO_MORE_DOCS;
 
         minDistance = query.getMinDistance();
         maxDistance = query.getMaxDistance();