Switch to flow map when emitting an empty block map

src/emitter.cpp

@@ -410,12 +410,18 @@ namespace YAML
 
 		EMITTER_STATE curState = m_pState->GetCurState();
 		FLOW_TYPE flowType = m_pState->GetCurGroupFlowType();
-		if(flowType == FT_BLOCK)
-			assert(curState == ES_DONE_WITH_BLOCK_MAP_VALUE);
-		else if(flowType == FT_FLOW) {
-			m_stream << "}";
+		if(flowType == FT_BLOCK) {
+			// Note: block sequences are *not* allowed to be empty, but we convert it
+			//       to a flow sequence if it is
+			assert(curState == ES_DONE_WITH_BLOCK_MAP_VALUE || curState == ES_WAITING_FOR_BLOCK_MAP_ENTRY);
+			if(curState == ES_WAITING_FOR_BLOCK_MAP_ENTRY) {
+				unsigned curIndent = m_pState->GetCurIndent();
+				m_stream << IndentTo(curIndent) << "{}";
+			}
+		} else if(flowType == FT_FLOW) {
 			// Note: flow maps are allowed to be empty
 			assert(curState == ES_DONE_WITH_FLOW_MAP_VALUE || curState == ES_WAITING_FOR_FLOW_MAP_ENTRY);
+			m_stream << "}";
 		} else
 			assert(false);