What is a NullPointerException, and how do I fix it?

Question

My test automation returns NullPointerException.

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?

What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?

You may think this too generic and lacks details but similar question exists on Stackoverflow and given the number of votes it appears helpful to others.

Also, we have plenty of questions about this topic on this site:

• NullPointerException in RequestSpecification
• Seeing NullPointerException on running TestNG Selenium Framework
• java.lang.NullPointerException - at com.qa.factory.factory.DriverFactory.init_driver(DriverFactory.java:26)
• How to debug NullPointerException in selenium-java
• NullPointerException - how to fix it?
• NullPointerException when using @FindBy

While I understand that many of our posters here have little coding experience (see similar discussion on SQA Meta), I also notice that such questions are very specific to the author code base and environment. This makes answers to such questions very specific and thus hard to generilize to other setups.

With such a generic question I am looking for answers that will provide basic troubleshooting steps that can be used in many custom setups.

Answer 1

A NullPointerException generally means there's a variable somewhere in your code that hasn't been initialized and you are trying to perform operations on null.

In test automation code, this often happens when an element is not found, and a fluent coding style is used, such as in the pseudocode below:

driver.findElement(By.Id("myElement")).Click();

If driver.findElement() fails to find myElement, the value will be null, which means that the attempt to click actually resolved to:

null.Click();

Obviously this can't work, so a null pointer exception is thrown.

Answer 2

A NullPointerException (often abbreviated as NPE) is a common runtime error in programming languages like Java, C++, and others. It occurs when a program attempts to access or manipulate an object that has not been initialized or is set to

"null." In simple terms, it means that the program is trying to perform an operation on an object that doesn't exist or has not been assigned any value.

For Example:

#include <iostream>

int main() {
    int* ptr = nullptr; // Initializing a pointer to Null
    
    if (ptr != nullptr) {
        // Attempting to access the value of the pointer, which is Null
        std::cout << "Value of ptr: " << *ptr << std::endl;
    } else {
        std::cout << "Pointer is Null." << std::endl;
    }

    return 0;
}