The cause: The NullPointerException occurs when an uninitialized object is attempted to be accessed or updated in application code. This essentially signifies that the object reference has a null value and does not point anywhere.

The command line causing the error is System.out.println(strName.length()); strName is not checked and you need to make sure that it is not empty before use.

Solution: To resolve the NullPointerException in the example, the string strName should be verified for null or empty values before further use:

import org.apache.commons.lang3.StringUtils;

public class NullPointerExceptionExample {
    private static void printLen(String strName) {
        if (StringUtils.isNotEmpty(strName)) {
           System.out.println(strName.length());
        } else {
            System.out.println("Empty string");
        }
    }

    public static void main(String args[]) {
        String myStrName = null;
        printLen(myStrName);
    }
}