Handle sdf::Geometry::EMPTY in conversions (gazebosim#2430)

Signed-off-by: Nate Koenig <natekoenig@gmail.com>

Author: nkoenig

src/Conversions.cc

@@ -259,6 +259,10 @@ msgs::Geometry gz::sim::convert(const sdf::Geometry &_in)
       }
     }
   }
+  else if (_in.Type() == sdf::GeometryType::EMPTY)
+  {
+    out.set_type(msgs::Geometry::EMPTY);
+  }
   else
   {
     gzerr << "Geometry type [" << static_cast<int>(_in.Type())

src/Conversions_TEST.cc

@@ -1206,3 +1206,13 @@ TEST(Conversions, MsgsPluginToSdf)
   EXPECT_EQ(innerXml, sdfPlugins[1].Contents()[0]->ToString(""));
   EXPECT_EQ(innerXml2, sdfPlugins[1].Contents()[1]->ToString(""));
 }
+
+/////////////////////////////////////////////////
+TEST(Conversions, GeometryEmpty)
+{
+  sdf::Geometry geometry;
+  geometry.SetType(sdf::GeometryType::EMPTY);
+
+  auto geometryMsg = convert<msgs::Geometry>(geometry);
+  EXPECT_EQ(msgs::Geometry::EMPTY, geometryMsg.type());
+}