An internal error occurred during: "Updating Maven Project". java.lang.NullPointerException

I solved mine by deleting the .settings folder and .project file in the project and then reimporting the project.

For me worked the answer I found on CodeRanch, by user Maneesh Godbole:

1. Close eclipse.
2. Navigate to your "workspace" folder
3. Ensure the setting on your OS to view hidden files is turned on
4. Identify and delete the .metadata directory
5. Restart eclipse
6. Import project

I've had the same problem in one of my modules.

Running "mvn eclipse:eclipse" in the console/cmd solved the problem for me.

In our instance of this problem, we had pom.xml files where the m2e-specific life cycle mapping configuration

<pluginManagement>
    <plugins>
        <plugin>
            <groupId>org.eclipse.m2e</groupId>
            <artifactId>lifecycle-mapping</artifactId>
            <version>1.0.0</version>
            <configuration>
                <lifecycleMappingMetadata>
...

did not have the <version>1.0.0</version> part. When doing a Maven -> Update Project..., this causes the reported NullPointerException without a stack trace. When using a fresh Import... -> Existing Maven Projects, the same exception occurred, but with a stack trace that led me to find the above.

(This is with m2e 1.6.1.20150625-2338 in Eclipse Luna Service Release 2 (4.4.2).)

In case it helps anyone, in addition to deleting .settings and .project, I had to delete .classpath and .factorypath before being able to import the project successfully into Eclipse.