Null argument not allowed

Question

Hi team, 
 
 I am going through this appian tutorial Process Modeling Tutorial - Appian 21.2 but error in expenseReportSummary Interface like this " Could not display interface. Please check definition and inputs. Interface Definition: Expression evaluation error at function 'user' [line 5]: Null argument not allowed". 
 i have interface 
 { a!textField( label: "Requester", labelPosition: "ADJACENT", value: user(ri!expenseReport['recordType!{618f143c-4310-4256-a9c3-b96fe7161fcf}AT Expense Report.fields.{pp}pp.{initiator}initiator'], "firstName") & " " & user(ri!expenseReport['recordType!{618f143c-4310-4256-a9c3-b96fe7161fcf}AT Expense Report.fields.{pp}pp.{initiator}initiator'],"lastName") ), a!textField( label: "Amount", labelPosition: "ADJACENT", value: ri!expenseReport['recordType!{618f143c-4310-4256-a9c3-b96fe7161fcf}AT Expense Report.fields.{expenseAmount}expenseAmount'], readOnly: true ), a!textField( label: "Date", labelPosition: "ADJACENT", value: ri!expenseReport['recordType!{618f143c-4310-4256-a9c3-b96fe7161fcf}AT Expense Report.fields.{expenseDate}expenseDate'], readOnly: true ) } 
 
 error in user()

Thanks, 
 kiran

Selvakumar Kumarasamy · Answer

Hi kirank , 
 The user() function does not allow null arguments. Hence you're getting this error. Try placing a null check for the arguments before the user() function. Also, make sure that you pass the data to the input of the interface for testing. 
 Sample code: 
 a!textField(
 label: "Requester",
 labelPosition: "ADJACENT",
 value: if(
 isnull(
 ri!expenseReport['recordType!{618f143c-4310-4256-a9c3-b96fe7161fcf}.fields.{pp}.{initiator}']
 ),
 "Username is unavailable", /*Customized message*/
 user(
 ri!expenseReport['recordType!{618f143c-4310-4256-a9c3-b96fe7161fcf}.fields.{pp}.{initiator}'],
 "firstName"
 ) & " " & user(
 ri!expenseReport['recordType!{618f143c-4310-4256-a9c3-b96fe7161fcf}.fields.{pp}.{initiator}'],
 "lastName"
 )
 )
)

Null argument not allowed

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