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Exception in modal window when setting page message



A modal window is used to enter data. Validation rules are used to ensure that the data meets a set criteria and are triggered when the modal window is submitted.

When executing a Validation rule, the below generic error message displays instead of the Validation error:

Status: Fail.
There has been an issue; please consult your system administrator.

Error Messages

[WebContainer : 1] [TABTHREAD3] [ ] [xxxx:01.01.01] (xxxx.When) ERROR prpchost|xx.xx.xx.xx XXXX - Exception caught while evaluating when
    at com.pegarules.generated.when.ra_when__55a6ae0baebfbccc191949c431e2f002.evaluate( ~[?:?]
    at com.pega.pegarules.session.internal.mgmt.Executable.evaluateWhen( ~[prprivate.jar:?]
    at com.pega.pegarules.session.internal.mgmt.Executable.invokeWhen( ~[prprivate.jar:?]
    at ~[prprivate.jar:?]
    at ~[prprivate.jar:?]
    at ~[prprivate.jar:?]
    at ~[prprivate.jar:?]
    at com.pega.pegarules.session.internal.mgmt.autostreams.AutoStreamRuntimeImpl.evaluateWhen( ~[prprivate.jar:?]
    at com.pega.pegarules.generation.internal.assembly.jspwhen.ProcessWhenExpression.evaluateCompiledWhen( ~[prprivate.jar:?]
2018-03-23 12:23:09,450 [    WebContainer : 1] [TABTHREAD3] [                    ] [     xxxx:01.01.01] (xxxx.Stream) ERROR prpchost|xx.xx.xx.xx XXXX - Section 'MySection' execution error on page '' of  class 'XXXX-XXXX-XXXX-XXXX'.
java.lang.RuntimeException: Component stack mismatch { [...] }
    at com.pega.pegarules.session.internal.mgmt.autostreams.uicomponent.json.UIComponentRuntimeImpl.finishProcess( ~[prprivate.jar:?]

Steps to Reproduce

  1. Create a When rule which accepts a parameter of type 'Page Name'.
  2. Reference this When rule on a section (for example, to control Visibility).
  3. In a flow, do not set the parameter required for the When rule (to force the error).
  4. Start the flow on a User portal.

Root Cause

An issue in the custom application code or rules. The issue occurred due to the following reasons:
  1. A When rule was setup that accepted a parameter of 'Page Name'.
  2. The Required parameter was not provided (or an incorrect parameter was provided; where the underlying named page did not exist).
  3. If the When rule was used on a Stream rule (such as a section); the issue manifested as a 'Component stack mismatch'.


Perform the following local-change:

Provide the correct Page Name for any When rule that requires a parameter of type 'Page Name'.

On the When Rule, check for the existence of the Page using the out-of-the-box @PageExists function before testing the Properties.

For example, add a new test in the When rule (set this as the first test) to ensure that the page exists using the below expression:

@PageExists(Param.PageReference) -> true

Published August 19, 2019 - Updated December 2, 2021

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