Fix NPE when Spoon launch with a wrong path for input resource

src/main/java/spoon/support/compiler/FileSystemFile.java

@@ -48,11 +48,13 @@ public FileSystemFile(File file) {
 
 	public InputStream getContent() {
 		try {
+			if (!this.file.exists()) {
+				throw new FileNotFoundException("The following file does not exist: " + this.file.getCanonicalPath());
+			}
 			return new FileInputStream(file);
-		} catch (FileNotFoundException e) {
-			Launcher.LOGGER.error(e.getMessage(), e);
+		} catch (IOException e) {
+			throw new SpoonException(e);
 		}
-		return null;
 	}
 
 	public String getName() {

src/test/java/spoon/test/api/FileSystemFolderTest.java

@@ -3,10 +3,16 @@
 import static org.junit.Assert.assertTrue;
 
 import java.io.File;
+import java.io.FileNotFoundException;
 import java.util.List;
 
+import org.junit.Rule;
 import org.junit.Test;
 
+import org.junit.rules.ExpectedException;
+import spoon.Launcher;
+import spoon.LauncherTest;
+import spoon.SpoonException;
 import spoon.compiler.SpoonFolder;
 import spoon.support.compiler.FileSystemFolder;
 
@@ -19,4 +25,16 @@ public void jarFileIsNotSubfolder() {
 		List<SpoonFolder> subFolders = folder.getSubFolders();
 		assertTrue(subFolders.isEmpty());
 	}
+
+	@Test
+	public void testLauncherWithWrongPathAsInput() {
+		Launcher spoon = new Launcher();
+		spoon.addInputResource("./src/wrong/direction/File.java");
+		try {
+			spoon.buildModel();
+		} catch (SpoonException spe) {
+			Throwable containedException = spe.getCause().getCause();
+			assertTrue(containedException instanceof FileNotFoundException);
+		}
+	}
 }