dotter: Add default variable template helper

.dotter/helpers/var_with_default.rhai

@@ -0,0 +1,12 @@
+// tests the type of variable passed in
+// if 'no' type (does not exist or cant be parsed)
+// we return the second, 'default' variable
+
+fn choose(a, b) {
+    if type_of(a) != "()" {
+        return a;
+    }
+    return b;
+}
+
+choose(params[0], params[1])