Fixes

Author: franzpoeschel

examples/14_toml_template.cpp

@@ -20,6 +20,10 @@ void write()
     std::string config = R"(
 {
   "iteration_encoding": "variable_based",
+  "json": {
+    "dataset": {"mode": "template"},
+    "attribute": {"mode": "short"}
+  },
   "toml": {
     "dataset": {"mode": "template"},
     "attribute": {"mode": "short"}

src/IO/JSON/JSONIOHandlerImpl.cpp

@@ -643,14 +643,16 @@ void JSONIOHandlerImpl::createDataset(
             break;
         }
         case IOMode::Template:
-            if (parameter.extent != Extent{0})
+            if (parameter.extent != Extent{0} &&
+                parameter.dtype != Datatype::UNDEFINED)
             {
                 dset["extent"] = parameter.extent;
             }
             else
             {
                 // no-op
-                // If extent is empty, don't bother writing it
+                // If extent is empty or no datatype is defined, don't bother
+                // writing it
             }
             break;
         }