# Ignition OPCUA Server "Null" Datatype **URL:** \ **Category:** Ignition\ **Tags:** opcua\ **Created:** [July 2, 2026, 2:22pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249 "2026-07-02T14:22:38Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![alvise.garbin](https://avatars.discourse-cdn.com/v4/letter/a/57b2e6/32.png) [@alvise.garbin](https://forum.inductiveautomation.com/u/alvise.garbin)\ **Post date:** [July 2, 2026, 2:22pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249/1 "2026-07-02T14:22:38Z")
Hello everyone, I am currently experiencing an issue with the "Null" data type on an Ignition OPC UA Server. I have created a string tag (both inside a UDT and standalone) with its value source set as **"Memory"**. The tag is also initialized with a default value of `""` (empty string). The problem occurs when I connect to the Ignition OPC UA Server using an external OPC UA client (UaExpert). The client sees the tag's data type as **Null**. I found a temporary workaround: if I click to edit the tag's value, type nothing, and lose focus, the OPC UA client suddenly displays the correct data type (String). However, after some time, it randomly resets back to **Null**. Has anyone encountered this issue before? Is there a permanent fix or remedy for this? Thanks in advance! ![UaExpert reading the value](https://us1.discourse-cdn.com/inductiveautomation/optimized/3X/6/c/6ce64cd6e3033705d3daa10d457f2f9b94fb9836_2_690x31.png) ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [July 2, 2026, 2:35pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249/2 "2026-07-02T14:35:17Z")
Have you deliberately set the memory tag's datatype to string? (Show the tag editor.) Also, what (precise) version of Ignition? ---
**Author:** ![alvise.garbin](https://avatars.discourse-cdn.com/v4/letter/a/57b2e6/32.png) [@alvise.garbin](https://forum.inductiveautomation.com/u/alvise.garbin)\ **Post date:** [July 2, 2026, 2:42pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249/3 "2026-07-02T14:42:04Z")
I'm currently using Ignition gateway 8.3.4 and I confirm that I've set the tag's datatype to string from the Tag editor. Here's the tag editor. ![Screenshot 2026-07-02 163908](https://us1.discourse-cdn.com/inductiveautomation/original/3X/4/1/4172b2d7a3c7bb8b5a98f3cc09102b12d3a83827.png) ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [July 2, 2026, 2:44pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249/4 "2026-07-02T14:44:41Z")
The DataType that UaExpert shows in the Data Access View is the type of the actual value received for that Monitored Item - it's not the value of the DataType attribute of the Node identified by that NodeId. What this means is that the Ignition tag value is `null` for some reason. ---
**Author:** ![alvise.garbin](https://avatars.discourse-cdn.com/v4/letter/a/57b2e6/32.png) [@alvise.garbin](https://forum.inductiveautomation.com/u/alvise.garbin)\ **Post date:** [July 2, 2026, 2:55pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249/5 "2026-07-02T14:55:43Z")
Perfect. Since this "absence" of the data type is causing problems on the customer's OPC UA client, is there any known workaround? For example, would setting a specific default value like " " or "xx" instead of `""` help prevent this? ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [July 2, 2026, 3:06pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249/6 "2026-07-02T15:06:05Z")
Well, to be clear, the actual DataType attribute should still show up as String at all times. You'd need to find this node in the attributes pane of UaExpert to verify that. It sounds like this client has a problem handling `null` values. As a workaround you could try putting in different empty-looking or sentinel strings in Ignition. I'm not sure if it's intentional whether a memory tag with an empty string value reverts back to `null` or if there's something else going on there - @ggross might have a better idea. It's also worth chasing down the bug in the customer's client. It should be able to handle `null` values. ---
**Author:** ![ggross](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/ggross/32/12668_2.png) [@ggross](https://forum.inductiveautomation.com/u/ggross)\ **Post date:** [July 7, 2026, 2:38pm UTC](https://forum.inductiveautomation.com/t/ignition-opcua-server-null-datatype/116249/7 "2026-07-07T14:38:14Z")
> [@Kevin.Herron](#): > > I'm not sure if it's intentional whether a memory tag with an empty string value reverts back to `null` or if there's something else going on there Empty Strings within an Ignition Tag of a String datatype are always considered a empty string. The two ways that a `null` value can be set on tags are: 1. When initially creating a tag, if no value is set for `value` (and `defaultValue` if using 8.3) then a `null` value will be the default value. 2. After any change to the value, performing a `system.tag.writeBlocking('', None)` will also set a `null` value that will persist. For memory tags, you can check the SQLite DB that persists tag values located at `/data/config/ignition/tags/valueStore.idb` in 8.3 versions of Ignition to confirm that the `null` value is persisted. The `TAG_VALUE_STORE` table's `nullValue` column will be 1 if `null` is persisted.