[MNG-7679] [REGRESSION] Build fails when executing a single mojo without a POM

This closes #244

its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng7679SingleMojoNoPomTest.java

@@ -0,0 +1,65 @@
+package org.apache.maven.it;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.File;
+
+import org.apache.maven.shared.verifier.Verifier;
+import org.apache.maven.shared.verifier.util.ResourceExtractor;
+import org.junit.jupiter.api.Test;
+
+/**
+ * This is a test set for <a href="https://issues.apache.org/jira/browse/MNG-7679">MNG-7679</a>.
+ * Executing single mojo without POM should not NPE.
+ *
+ */
+class MavenITmng7679SingleMojoNoPomTest
+    extends AbstractMavenIntegrationTestCase
+{
+
+    public MavenITmng7679SingleMojoNoPomTest()
+    {
+        // affected Maven versions: 3.8.7, 3.9.0, 4.0.0-alpha-4
+        super( "(,3.8.7)(3.8.7,3.9.0),(3.9.0,4.0.0-alpha-4),(4.0.0-alpha-4,)" );
+    }
+
+    /**
+     * Verify that maven invocation works (no NPE/error happens).
+     *
+     * @throws Exception in case of failure
+     */
+    @Test
+    void testSingleMojoNoPom()
+        throws Exception
+    {
+        File testDir = ResourceExtractor.simpleExtractResources( getClass(), "/mng-7679" );
+
+        Verifier verifier = newVerifier( testDir.getAbsolutePath() );
+        verifier.addCliArgument( "install:install-file" );
+        verifier.addCliArgument( "-Dfile=mng-7679.txt" );
+        verifier.addCliArgument( "-DgroupId=org.apache.maven.it.mng7679" );
+        verifier.addCliArgument( "-DartifactId=artifact" );
+        verifier.addCliArgument( "-Dversion=1.0.0" );
+        verifier.addCliArgument( "-Dpackaging=jar" );
+        verifier.execute();
+        verifier.verifyErrorFreeLog();
+    }
+
+}

its/core-it-suite/src/test/java/org/apache/maven/it/TestSuiteOrdering.java

@@ -105,6 +105,7 @@ public class TestSuiteOrdering implements ClassOrderer
          * the tests are to finishing. Newer tests are also more likely to fail, so this is
          * a fail fast technique as well.
          */
+        suite.addTestSuite( MavenITmng7679SingleMojoNoPomTest.class );
         suite.addTestSuite( MavenITmng7629SubtreeBuildTest.class );
         suite.addTestSuite( MavenITmng7606DependencyImportScopeTest.class );
         suite.addTestSuite( MavenITmng6609ProfileActivationForPackagingTest.class );

its/core-it-suite/src/test/resources/mng-7679/mng-7679.txt

@@ -0,0 +1 @@
+test