DMN Decision Table always returns null for the output variable, even when the input explicitly matches a rule.

Camunda 8 Topics Discussion & Questions
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  • It’s a cloud trial version.

  • Camunda Platform 8.7.0

  • Core Problem Symptom:

    • “DMN Decision Table always returns null for the output variable, even when the input explicitly matches a rule.”
    • “Camunda Operate’s Decision Instance view consistently shows inputs (e.g., userConsent: true or myInput: true), but the ‘Outputs’ section remains empty (no rule or name displayed), and no rule is highlighted in the decision table.”

  • Comprehensive Troubleshooting Steps You’ve Already Taken (This is CRUCIAL for them):

    • “Confirmed form variable (userConsent/myInput) is correctly passed as a boolean (true/false) into the BPMN process and is visible as input to the Business Rule Task in Operate.”
    • “Verified Business Rule Task zeebe:ioMapping for input and output, and zeebe:calledDecision are correct in BPMN XML.”
    • “Verified DMN XML: inputExpression matches process variable name (userConsent/myInput), typeRef=‘boolean’. Output name=‘Result’/myOutput, typeRef=‘string’.”
    • “Manually re-typed true and false literals within DMN inputEntry tags in a plain text editor to eliminate hidden characters/encoding issues.”
    • “Removed informationRequirement and inputData elements from DMN for simplification.”
    • “Confirmed DMN uses default Unique hit policy.”
    • “Performed multiple clean redeployments, including deleting and recreating the entire cluster, then deploying BPMN/DMN/Form together as a single, fresh deployment.”
    • “The issue persists even with an ultra-minimal, brand-new, manually-typed test case (simplified form using a checkbox for input, BPMN, and DMN with single boolean input and string output).”

  • Attached Test Files:

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Hi @Patricio_Pozo_T

You are currently using a checkbox group in your form that is bound to an array.
Please try using a single checkbox input instead, bound to a boolean variable.

Attached is a corrected version of the form

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MyTestForm.form (451 Bytes)

1 Like
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Hello, thank you that did work, although what I realy need is to validate a radio button, wich does always result in ‘null’.
In this same example , how would I use a radio button for business rule validation?

4

Hi @Patricio_Pozo_T

You can use a radio group with static string values and change the input mapping accordingly

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image1492×658 27.3 KB

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test.bpmn (3.5 KB)
MyTestForm.form (638 Bytes)