Fix NPE when empty working dir

src/main/java/spoon/support/compiler/jdt/JDTBasedSpoonCompiler.java

@@ -392,7 +392,7 @@ protected CompilationUnitDeclaration[] buildUnits(JDTBuilder jdtBuilder, SpoonFo
 					.classpathOptions(new ClasspathOptions().encoding(this.encoding).classpath(classpath)) //
 					.complianceOptions(new ComplianceOptions().compliance(javaCompliance)) //
 					.advancedOptions(new AdvancedOptions().preserveUnusedVars().continueExecution().enableJavadoc()) //
-					.sources(new SourceOptions().sources()) // no sources, handled by the JDTBatchCompiler
+					.sources(new SourceOptions().sources(sourcesFolder.getAllJavaFiles())) // no sources, handled by the JDTBatchCompiler
 					.build();
 		} else {
 			args = jdtBuilder.build();

src/test/java/spoon/LauncherTest.java

@@ -1,13 +1,16 @@
 package spoon;
 
 import org.junit.Assert;
+import org.junit.Ignore;
 import org.junit.Test;
 
 import spoon.compiler.Environment;
 import spoon.reflect.visitor.DefaultJavaPrettyPrinter;
 import spoon.support.JavaOutputProcessor;
 
 import java.io.File;
+import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -68,4 +71,25 @@ public void testInitEnvironment() throws Exception {
 
 	}
 
+	@Test
+	public void testLauncherInEmptyWorkingDir() throws Exception {
+
+		// Contract: Spoon can be launched in an empty folder as a working directory
+		// See: https://github.com/INRIA/spoon/pull/1208
+		// This test does not fail (it's not enough to change user.dir we should launch process inside that dir) but it explains the problem
+		final Launcher launcher = new Launcher();
+		Path path = Files.createTempDirectory("emptydir");
+
+		String oldUserDir = System.getProperty("user.dir");
+		System.setProperty("user.dir", path.toFile().getAbsolutePath());
+
+		// path should exist, otherwise it would crash on a filenotfoundexception before showing the bug
+		launcher.addInputResource(oldUserDir+"/src/test/java/spoon/LauncherTest.java");
+		try {
+			launcher.buildModel();
+		} finally {
+			System.setProperty("user.dir", oldUserDir);
+		}
+	}
+
 }