Cannot resolve symbol 'NotBlank'

This error message usually occurs when you try to use a method or annotation that is not recognized by your code.

In particular, "NotBlank" is an annotation from the Apache Commons library that can be used to mark a string parameter as not null and not consisting only of whitespace characters.

To resolve this issue, you need to make sure that you have imported the necessary dependencies in your code. Specifically, you should add the following import statement at the top of your Java file:

import org.apache.commons.lang3.StringUtils;

This will allow you to use the NotBlank annotation in your code. Make sure that you have also included the Apache Commons library as a dependency in your project's build file (such as pom.xml for Maven or build.gradle for Gradle).