Invalid Template. Unable to process

[Paul_Iowa]

In a Condition I reference a manual trigger field (subject/body) using this expression:  

lastIndexOf(triggerOutputs()?['bodysubject'],'-') IS EQUAL TO IndexOf(triggerOutputs()?['bodysubject'],'-')

I get this error:

Unable to process template language expressions for action 'Check_If_Old_Subject_Format' at line '1' and column '25728': 'The template language function 'lastIndexOf' expects its first parameter to be of type string. The provided value is of type 'Null'. Please see https://aka.ms/logicexpressions#lastindexof for usage details.'.

Why?  The trigger 'bodysubject' is a text.  Is that different a 'string"?  'String' isn't an option in the manual trigger step.

Thanks very much.

Details in trigger:

{

  "type": "object",

  "properties": {

    "text": {

      "title": "bodysubject",

      "type": "array",

      "x-ms-dynamically-added": true,

      "description": "Subject line from \"Zoom Joined\" email",

      "items": {

        "enum": [

          "Susie has joined your meeting - XXXXXXX Britt/Kellie 60 minute XXXXXX Session (277-48-18-Z1)",

          "John Doe has joined your meeting - XXXX 18's Zoom Meeting"

        ],

        "type": "string"

      },

      "x-ms-content-hint": "TEXT"

    }

  },

  "required": [

    "text"

  ]

}

[v-bofeng-msft]

Hi @Paul_Iowa :

Could you tell me:

• When the user triggers the flow, will multiple values be selected for bodysubject?

I assume the user selects only one value.

Firstly,let me explain why you encountered this problem.

The point is the value of triggerOutputs()?['bodysubject'] is an array.Because you set multiple selections in the trigger, its return value is an array.The first parameter of the lastIndexOf and IndexOf functions must be a string, so your flow will report an error.

Secondly,I suggest you use [0] to extract the value of the first item in the array to solve this problem.For example

lastIndexOf(triggerBody()['text'][0],'-')

IS EQUAL TO

IndexOf(triggerBody()['text'][0],'-')

Best Regards,

Bof

[Paul_Iowa · Accepted solution]

Wonderful! Solved!

And your help @v-bofeng-msft has gotten me past something else as well. 

My main issue was that I should have selected "Drop-down list of options" in the manual trigger.  I only needed one result. 

With only one result my original expressions work!

IndexOf(triggerOutputs()?['bodysubject'],'-')

IndexOf(triggerOutputs()?['bodysubject'],'-')

If I remove the [0] from your expressions (because it's no longer a set) it also works!

lastIndexOf(triggerBody()['text'],'-')
IndexOf(triggerBody()['text'],'-')

PS - 

The answer to your question: I was temporarily using the "Manual Trigger" because the Outlook "Get an email" trigger was not working and I needed to move on and test other parts of my flow.  Now that you've helped me I can go back and tackle that issue. 

Thanks very much!