Only empty TechTree when there exists a BuildDescription

src/TechTree.cpp

@@ -31,13 +31,18 @@ void TechTree::onStart()
     {
         TypeData & data = pair.second;
 
+        const std::vector<BuildDescription> & howToBuild = tree.HowToBuild(pair.first.getAPIUnitType());
+
+        if (howToBuild.empty())
+        {
+            continue;
+        }
+
         data.whatBuilds.clear();
         data.requiredUnits.clear();
         // TODO: Support for upgrades, is it possible via JSON? Is the hard coded information correct?
         data.requiredUpgrades.clear();
 
-        const std::vector<BuildDescription> & howToBuild = tree.HowToBuild(pair.first.getAPIUnitType());
-
         for (const BuildDescription & description : howToBuild)
         {
             data.whatBuilds.push_back(UnitType(description.producer_type, m_bot));
@@ -63,7 +68,6 @@ void TechTree::onStart()
         data.requiredUnits.clear();
         data.requiredUpgrades.clear();
 
-
         for (const ResearchDescription & description : tree.HowToResearch(id))
         {
             data.buildAbility = description.ability_used;