data: fix construction from empty model

src/multibody/data.hxx

@@ -96,7 +96,7 @@ namespace pinocchio
   , impulse_c()
   , staticRegressor(3,4*(model.njoints-1))
   , jointTorqueRegressor(model.nv,10*(model.njoints-1))
-  , kinematic_hessians(6,model.nv,model.nv)
+  , kinematic_hessians(6,std::max(1,model.nv),std::max(1,model.nv)) // the minimum size should be 1 for compatibility reasons
   {
     typedef typename Model::JointIndex JointIndex;
     

unittest/data.cpp

@@ -13,6 +13,12 @@ using namespace pinocchio;
 
 BOOST_AUTO_TEST_SUITE(BOOST_TEST_MODULE)
 
+  BOOST_AUTO_TEST_CASE(test_empty_model)
+  {
+    Model empty_model;
+    Data empty_data(empty_model);
+  }
+
   BOOST_AUTO_TEST_CASE(test_data_start_idx_v_fromRow)
   {
     Model model;