NPE when used in IDE as first phase of maven

[freedom1b2830]

Describe the bug
My idea was to run signature verification immediately after downloading the dependencies, so I set the validate phase.
when running mvn clean install it works fine.
When opening a project in eclipse it shows NPE

To Reproduce

1. create 2 projects(see pom.xml files below)
2. open projects in eclipse

Expected behavior
running the verification plugin after downloading dependencies

Additional context
There is no such behavior when used in maven.

error in:

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<artifactId>proj</artifactId>
	<parent>
		<groupId>proj</groupId>
		<artifactId>header</artifactId>
		<version>1.0</version>
	</parent>
</project>

parent:

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>proj</groupId>
	<artifactId>header</artifactId>
	<version>1.0</version>
	<packaging>pom</packaging>

	
	</build>
		<pluginManagement>
			<plugins>
				<plugin>
					<groupId>org.simplify4u.plugins</groupId>
					<artifactId>pgpverify-maven-plugin</artifactId>
					<version>1.17.0</version>
				</plugin>
			</plugins>
		</pluginManagement>

			<plugin>
				<groupId>org.simplify4u.plugins</groupId>
				<artifactId>pgpverify-maven-plugin</artifactId>
				<configuration>
					<keysMapLocation>${PGP_MAP}</keysMapLocation>
					<verifyPlugins>true</verifyPlugins>
					<verifyAtypical>true</verifyAtypical>
					<suppressSignatureOkLogging>true</suppressSignatureOkLogging>
					<verifySnapshots>true</verifySnapshots>
					<verifyPluginDependencies>true</verifyPluginDependencies>
				</configuration>
				<executions>
					<execution>
						<id>download</id>
						<phase>validate</phase>
						<goals>
							<goal>go-offline</goal>
							<goal>check</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
		</plugins>
	</build>
</project>

Failed to execute mojo org.simplify4u.plugins:pgpverify-maven-plugin:1.17.0:check {execution: download} (org.simplify4u.plugins:pgpverify-maven-plugin:1.17.0:check:download:validate)

org.eclipse.core.runtime.CoreException: Failed to execute mojo org.simplify4u.plugins:pgpverify-maven-plugin:1.17.0:check {execution: download}
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeMojo(MavenExecutionContext.java:340)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.lambda$0(MavenExecutionContext.java:291)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:394)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:275)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:290)
	at org.eclipse.m2e.core.project.configurator.MojoExecutionBuildParticipant.build(MojoExecutionBuildParticipant.java:57)
	at org.eclipse.m2e.core.internal.builder.MavenBuilderImpl.lambda$2(MavenBuilderImpl.java:153)
	at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:986)
	at org.eclipse.m2e.core.internal.builder.MavenBuilderImpl.build(MavenBuilderImpl.java:133)
	at org.eclipse.m2e.core.internal.builder.MavenBuilder$1.method(MavenBuilder.java:164)
	at org.eclipse.m2e.core.internal.builder.MavenBuilder$1.method(MavenBuilder.java:1)
	at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.lambda$1(MavenBuilder.java:109)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:394)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:228)
	at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.lambda$0(MavenBuilder.java:100)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:394)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:275)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:214)
	at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.execute(MavenBuilder.java:83)
	at org.eclipse.m2e.core.internal.builder.MavenBuilder.build(MavenBuilder.java:192)
	at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:1079)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:296)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:352)
	at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:441)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:444)
	at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:555)
	at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:503)
	at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:585)
	at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:207)
	at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:300)
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution download of goal org.simplify4u.plugins:pgpverify-maven-plugin:1.17.0:check failed: Cannot invoke "org.apache.maven.execution.ProjectDependencyGraph.getUpstreamProjects(org.apache.maven.project.MavenProject, boolean)" because the return value of "org.apache.maven.execution.MavenSession.getProjectDependencyGraph()" is null
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:133)
	at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeMojo(MavenExecutionContext.java:338)
	... 32 more
Caused by: java.lang.NullPointerException: Cannot invoke "org.apache.maven.execution.ProjectDependencyGraph.getUpstreamProjects(org.apache.maven.project.MavenProject, boolean)" because the return value of "org.apache.maven.execution.MavenSession.getProjectDependencyGraph()" is null
	at org.simplify4u.plugins.skipfilters.ReactorDependencySkipper.<init>(ReactorDependencySkipper.java:39)
	at org.simplify4u.plugins.AbstractVerifyMojo.prepareDependencyFilters(AbstractVerifyMojo.java:229)
	at org.simplify4u.plugins.AbstractVerifyMojo.executeConfiguredMojo(AbstractVerifyMojo.java:150)
	at org.simplify4u.plugins.AbstractPGPMojo.execute(AbstractPGPMojo.java:177)
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:126)
	... 33 more

[slawekjaranowski]

Issue can be caused by wrong eclipse implementation.

Despite, we can protect it in ReactorDependencySkipper - simply we can set an empty list for upstreamProjects.

[slawekjaranowski]

PR are welcome.