# \[BUG-7038\] OPC path inconsistently working in UDT definition **URL:** \ **Category:** Ignition\ **Tags:** ignition81\ **Created:** [July 7, 2022, 7:31am UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609 "2022-07-07T07:31:47Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![liam1](https://avatars.discourse-cdn.com/v4/letter/l/e68b1a/32.png) [@liam1](https://forum.inductiveautomation.com/u/liam1)\ **Post date:** [July 7, 2022, 7:31am UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609/1 "2022-07-07T07:31:47Z")
In my UDT instances, some tags in the definition show `null` in the OpcItmePath while others are not. They are all configured the same way All the parameters being passed are valid OPC paths ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/e/a/ea0b653b70c6ff60862b273de157aab9c140a8cb.png) This tag is showing `null` in the OPC path ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/f/1/f1ad0c73903116a9bfa87b6f9ed4dfe362255af8.png) This tag is working correctly ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/6/7/675380d8d4168a7d538aa68d55e1728d8c9f4fac.png) Can someone please tell me how to fix this please? ---
**Author:** ![hayden](https://avatars.discourse-cdn.com/v4/letter/h/91b2a8/32.png) [@hayden](https://forum.inductiveautomation.com/u/hayden)\ **Post date:** [July 7, 2022, 8:06am UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609/2 "2022-07-07T08:06:08Z")
On the OPC Item Path have you configured them to be expressions that link to your parameters. It looks like the first has no path and has errored while the second you’ve selected the OPC path correctly. Can you show the expression in UDT ---
**Author:** ![liam1](https://avatars.discourse-cdn.com/v4/letter/l/e68b1a/32.png) [@liam1](https://forum.inductiveautomation.com/u/liam1)\ **Post date:** [July 7, 2022, 8:56am UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609/4 "2022-07-07T08:56:18Z")
![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/a/da68c46a2b9d3f432050f44c11ec11f8f391ec66.png) ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/1/5/15db299e8254f68a698c479d8be9bee108f537c0.png) ---
**Author:** ![liam1](https://avatars.discourse-cdn.com/v4/letter/l/e68b1a/32.png) [@liam1](https://forum.inductiveautomation.com/u/liam1)\ **Post date:** [July 7, 2022, 10:28am UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609/5 "2022-07-07T10:28:05Z")
Okay, I figured out what the issue was, If the parameter name contains a `-` then the value does not get passed through. This has to be a bug that needs to be fixed. ---
**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 7, 2022, 11:57am UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609/6 "2022-07-07T11:57:59Z")
No, not a bug. Or rather the bug is that Ignition allowed you to use a hyphen in a parameter name. ---
**Author:** ![liam1](https://avatars.discourse-cdn.com/v4/letter/l/e68b1a/32.png) [@liam1](https://forum.inductiveautomation.com/u/liam1)\ **Post date:** [September 7, 2023, 11:57am UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609/7 "2023-09-07T11:57:54Z")
Maybe the documentation can be updated to include a list of characters that should be avoided when creating parameter names. ---
**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:** [September 7, 2023, 12:02pm UTC](https://forum.inductiveautomation.com/t/bug-7038-opc-path-inconsistently-working-in-udt-definition/61609/8 "2023-09-07T12:02:52Z")
Just make your parameter names (and any other names) in Ignition follow the typical rule for variable names in programming and you will be fine. (Alphanumeric plus underscore, but no leading decimal digit.)