UiPath-ADPv1 Advanced Debugging Practice Question
You are debugging a UiPath Studio project that throws a System.NullReferenceException intermittently inside a Try Catch placed in an invoked workflow. The Exception.Message is empty and the stack trace points to a private method within an imported custom activity library. You must determine which activity in the workflow passed the null object into that library before the exception is thrown. Which debugging technique should you use?
⚠ Common exam trap
The trap here is assuming that Verbose logging or the Watch panel can reveal argument values inside a compiled custom library, when only a conditional breakpoint plus Step Into can intercept the null before it reaches library code.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set a conditional breakpoint on the activity that invokes the custom library, using a condition that evaluates the arguments for null, then use Step Into to enter the library code.
Because the exception surfaces inside compiled library code with an empty message, the fastest reliable path is to stop execution precisely when a null argument is about to be passed. A conditional breakpoint on the invoking activity achieves that, and stepping into the library call confirms which parameter is null and which upstream activity produced it. This avoids fruitless manual stepping and does not depend on logging that cannot see into the library.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add the custom library assembly to the Watch panel and inspect its public static fields while the workflow runs in Debug mode.
Why it's wrong here
The Watch panel evaluates expressions against variables and arguments in the current workflow scope, not arbitrary internal state of an imported assembly. A NullReferenceException raised inside a private method is not observable through watching public static fields, and the null value originates from a workflow argument, so this approach cannot identify the responsible activity.
- ✗
Enable the Highlight Elements option and run the workflow in Debug mode so each UI interaction is visually highlighted before it executes.
Why it's wrong here
Highlight Elements only draws attention to UI automation activities as they run; it provides no visibility into argument values passed to a custom activity library. The failure here is a null object reference inside compiled library code, not a missing or misidentified UI element, so visual highlighting cannot reveal which argument was null or when the null was introduced.
- ✗
Set the project's logging level to Verbose and re-run the process, then search the Output panel for entries containing the library's namespace.
Why it's wrong here
Verbose logging records activity execution and messages emitted by the workflow, but it does not log argument values passed into third-party library methods or internal method calls. The exception message is empty, so Output will not name the null argument, and increasing log verbosity alone will not pinpoint which upstream activity supplied the null reference.
- ✓
Set a conditional breakpoint on the activity that invokes the custom library, using a condition that evaluates the arguments for null, then use Step Into to enter the library code.
Why this is correct
A conditional breakpoint that only pauses when an argument is null stops execution exactly at the offending invocation, and Step Into lets you follow execution into the custom library to confirm which argument is null. This isolates the null source without manually stepping through every prior activity, which is essential when the exception is intermittent and the message is empty.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official UiPath exam blueprint
This UiPath-ADPv1 practice question is part of Courseiva's free UiPath certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the UiPath-ADPv1 exam.