UiPath Certified Professional - Developer Track UiPath-ADAv1 Question # 10 Topic 2 Discussion

Understanding the Error:

The runtime execution error shown in the image is:

pgsql

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Message: Object reference not set to an instance of an object.

Exception Type: System.NullReferenceException

This error occurs when trying to access or modify an object that has not been initialized.

Step-by-Step Breakdown of the Issue:

What is Happening in the Workflow?

The developer is trying to assign a value to the dictionary using:

PinMapping["John"] = "1195488487"

Then, they attempt to log the count of the dictionary items:

String.Concat(PinMapping.Count, " people")

The error occurs at the Assign activity.

What Causes a NullReferenceException in a Dictionary?

If a dictionary variable is declared but not initialized, it remains Nothing (null).

Trying to access or modify a null object causes a NullReferenceException.

The dictionary should be initialized before adding key-value pairs.

Why Option B is Correct?

✅ The Dictionary was not initialized.

The error occurs because the dictionary PinMapping is not initialized before assigning values.

To fix this, the dictionary must be initialized before use:

PinMapping = New Dictionary(Of String, String)

PinMapping("John") = "1195488487"

This ensures that the dictionary is properly instantiated in memory before accessing it.

Why Other Options Are Incorrect?

❌ A. "The 'John' key was not present in the dictionary."

Incorrect because a missing key does not cause a NullReferenceException.

Instead, attempting to retrieve a missing key causes a KeyNotFoundException.

The error in the screenshot is caused by the dictionary itself being null, not a missing key.

❌ C. "The assign's set value syntax should be PinMapping["John"]."

Incorrect because the syntax used in the Assign activity is correct.

The dictionary is of type Dictionary(Of String, String), and "John" is correctly specified as a string key.

❌ D. "The assign's set value syntax should be PinMapping<"John">."

Incorrect because PinMapping<"John"> is not valid syntax in VB.NET.

The correct syntax is PinMapping("John") or PinMapping["John"] (in C# syntax).

How to Fix the Error?

✅ Solution: Initialize the Dictionary Before Using It

Before using the dictionary, add the following initialization step:

PinMapping = New Dictionary(Of String, String)

Then assign values as needed:

PinMapping("John") = "1195488487"

Final Answer and Explanation:

✅ Answer: B. The Dictionary was not initialized.

Key Takeaways:

A NullReferenceException occurs when trying to use an uninitialized dictionary.

Always initialize a dictionary before adding key-value pairs.

A missing key does not cause this error—it would result in a KeyNotFoundException.

✅ Reference:

???? UiPath Documentation – Dictionaries

???? VB.NET – Dictionary Initialization