Add error message for structs with no ksql tags

kstructs/structs.go

@@ -272,10 +272,12 @@ func getTagNames(t reflect.Type) (StructInfo, error) {
 		})
 	}
 
-	if len(info.byIndex) > 0 {
-		info.IsNestedStruct = true
+	if len(info.byIndex) == 0 {
+		return StructInfo{}, fmt.Errorf("the struct must contain at least one attribute with the ksql tag")
 	}
 
+	info.IsNestedStruct = true
+
 	return info, nil
 }
 

kstructs/structs_test.go

@@ -99,6 +99,18 @@ func TestStructToMap(t *testing.T) {
 
 		assert.NotEqual(t, nil, err)
 	})
+
+	t.Run("should return error for structs with no ksql tags", func(t *testing.T) {
+		_, err := StructToMap(struct {
+			Name string
+			Age  int `json:"age"`
+		}{
+			Name: "fake-name",
+			Age:  42,
+		})
+
+		assert.NotEqual(t, nil, err)
+	})
 }
 
 func TestFillStructWith(t *testing.T) {