review: fix NPE in MavenLauncher when there is no build section

src/main/java/spoon/MavenLauncher.java

@@ -341,16 +341,18 @@ private String getProperty(String key) {
 		 * @return the source version of the project
 		 */
 		public int getSourceVersion() {
-			for (Plugin plugin : model.getBuild().getPlugins()) {
-				if (!"maven-compiler-plugin".equals(plugin.getArtifactId())) {
-					continue;
-				}
-				Xpp3Dom configuration = (Xpp3Dom) plugin.getConfiguration();
-				Xpp3Dom source = configuration.getChild("source");
-				if (source != null) {
-					return Integer.parseInt(extractVariable(source.getValue()).substring(2));
+			if (model.getBuild() != null) {
+				for (Plugin plugin : model.getBuild().getPlugins()) {
+					if (!"maven-compiler-plugin".equals(plugin.getArtifactId())) {
+						continue;
+					}
+					Xpp3Dom configuration = (Xpp3Dom) plugin.getConfiguration();
+					Xpp3Dom source = configuration.getChild("source");
+					if (source != null) {
+						return Integer.parseInt(extractVariable(source.getValue()).substring(2));
+					}
+					break;
 				}
-				break;
 			}
 			String javaVersion = getProperty("java.version");
 			if (javaVersion != null) {

src/test/java/spoon/MavenLauncherTest.java

@@ -41,4 +41,10 @@ public void mavenLauncherOnANotExistingFileTest() {
 	public void mavenLauncherOnDirectoryWithoutPomTest() {
 		new MavenLauncher("./src", MavenLauncher.SOURCE_TYPE.APP_SOURCE);
 	}
+
+	@Test
+	public void mavenLauncherTestWithVerySimpleProject() {
+		MavenLauncher launcher = new MavenLauncher("./src/test/resources/maven-launcher/very-simple", MavenLauncher.SOURCE_TYPE.ALL_SOURCE);
+		assertEquals(1, launcher.getModelBuilder().getInputSources().size());
+	}
 }

src/test/resources/maven-launcher/very-simple/pom.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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 http://maven.apache.org/maven-v4_0_0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.foo.bar</groupId>
+    <artifactId>foobar</artifactId>
+    <version>1.0.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>foobar</name>
+</project>

src/test/resources/maven-launcher/very-simple/src/main/java/Test.java

@@ -0,0 +1,3 @@
+public class Test {
+    int field = 42;
+}