check there are hypos in stack vector before create translation options. constrained decoding works for syntax model

1 files changed, 8 insertions, 0 deletions

diff --git a/moses/ChartTranslationOptionList.cpp b/moses/ChartTranslationOptionList.cpp
index 757afd31b..52169c935 100644
--- a/moses/ChartTranslationOptionList.cpp
+++ b/moses/ChartTranslationOptionList.cpp
@@ -67,6 +67,14 @@ void ChartTranslationOptionList::Add(const TargetPhraseCollection &tpc,
     return;
   }
 
+  for (size_t i = 0; i < stackVec.size(); ++i) {
+	  const ChartCellLabel &chartCellLabel = *stackVec[i];
+	  size_t numHypos = chartCellLabel.GetStack().cube->size();
+	  if (numHypos == 0) {
+		  return; // empty stack. These rules can't be used
+	  }
+  }
+
   float score = ChartTranslationOptions::CalcEstimateOfBestScore(tpc, stackVec);
 
   // If the rule limit has already been reached then don't add the option