Fixed bundle not loading when empty variable is defined (#1552)

## Changes
Fixes #1544

## Tests
Added regression test

bundle/tests/variables/empty/databricks.yml

@@ -0,0 +1,7 @@
+variables:
+  a:
+    description: empty variable
+    default:
+
+bundle:
+  name: empty${var.a}

bundle/tests/variables_test.go

@@ -193,3 +193,9 @@ func TestVariableTargetOverrides(t *testing.T) {
 		})
 	}
 }
+
+func TestBundleWithEmptyVariableLoads(t *testing.T) {
+	b := load(t, "./variables/empty")
+	diags := bundle.Apply(context.Background(), b, mutator.SetVariables())
+	require.ErrorContains(t, diags.Error(), "no value assigned to required variable a")
+}

libs/dyn/convert/to_typed.go

@@ -282,6 +282,11 @@ func toTypedFloat(dst reflect.Value, src dyn.Value) error {
 }
 
 func toTypedInterface(dst reflect.Value, src dyn.Value) error {
+	if src.Kind() == dyn.KindNil {
+		dst.Set(reflect.Zero(dst.Type()))
+		return nil
+	}
+
 	dst.Set(reflect.ValueOf(src.AsAny()))
 	return nil
 }

libs/dyn/convert/to_typed_test.go

@@ -533,3 +533,10 @@ func TestToTypedAnyWithMap(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, map[string]any{"foo": "bar", "bar": "baz"}, out)
 }
+
+func TestToTypedAnyWithNil(t *testing.T) {
+	var out any
+	err := ToTyped(&out, dyn.NilValue)
+	require.NoError(t, err)
+	assert.Equal(t, nil, out)
+}