revelcGH-30: Handle files that are empty or lack a newline

pom.xml

@@ -376,6 +376,12 @@
       <plugin>
         <groupId>org.apache.rat</groupId>
         <artifactId>apache-rat-plugin</artifactId>
+        <configuration>
+          <excludes>
+            <exclude>src/test/resources/EmptyFile.java</exclude>
+            <exclude>src/test/resources/FileWithoutNewline.java</exclude>
+          </excludes>
+        </configuration>
         <executions>
           <execution>
             <id>check-licenses</id>

src/main/java/net/revelc/code/impsort/ImpSort.java

@@ -75,20 +75,25 @@ public ImpSort(final Charset sourceEncoding, final Grouper grouper, final boolea
 
   public Result parseFile(final Path path) throws IOException {
     String file = new String(Files.readAllBytes(path), sourceEncoding);
-    LineEnding fileLineEnding = LineEnding.determineLineEnding(file);
-    LineEnding impLineEnding;
-    if (lineEnding == LineEnding.KEEP) {
-      impLineEnding = fileLineEnding;
-    } else {
-      impLineEnding = lineEnding;
-    }
-    List<String> fileLines = Arrays.asList(file.split(fileLineEnding.getChars()));
     ParseResult<CompilationUnit> parseResult = new JavaParser().parse(file);
     CompilationUnit unit =
         parseResult.getResult().orElseThrow(() -> new IOException("Unable to parse " + path));
     Position packagePosition =
         unit.getPackageDeclaration().map(p -> p.getEnd().get()).orElse(unit.getBegin().get());
     NodeList<ImportDeclaration> importDeclarations = unit.getImports();
+    LineEnding impLineEnding = lineEnding;
+    List<String> fileLines = Collections.emptyList();
+    if (!file.isEmpty()) {
+      LineEnding fileLineEnding = LineEnding.determineLineEnding(file);
+      if (lineEnding == LineEnding.KEEP) {
+        impLineEnding = fileLineEnding;
+      }
+      if (lineEnding == LineEnding.UNKNOWN) {
+        fileLines = Collections.singletonList(file);
+      } else {
+        fileLines = Arrays.asList(file.split(fileLineEnding.getChars()));
+      }
+    }
     if (importDeclarations.isEmpty()) {
       return new Result(path, sourceEncoding, fileLines, 0, fileLines.size(), "", "",
           Collections.emptyList(), impLineEnding);

src/main/java/net/revelc/code/impsort/LineEnding.java

@@ -19,7 +19,7 @@
  */
 public enum LineEnding {
 
-  AUTO(System.lineSeparator()), KEEP(null), LF("\n"), CRLF("\r\n"), CR("\r"), UNKNOWN(null);
+  AUTO(System.lineSeparator()), KEEP(null), LF("\n"), CRLF("\r\n"), CR("\r"), UNKNOWN("");
 
   private final String chars;
 

src/test/java/net/revelc/code/impsort/FileTest.java

@@ -0,0 +1,58 @@
+/*
+ * Licensed 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.
+ */
+package net.revelc.code.impsort;
+
+import static org.junit.Assert.assertTrue;
+
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.junit.Test;
+
+/**
+ * Test class for special file cases.
+ */
+public class FileTest {
+
+  private static Grouper eclipseDefaults =
+      new Grouper("java.,javax.,org.,com.", "", false, false, true);
+
+  /**
+   * Test successfully parsing empty (0 byte) file.
+   */
+  @Test
+  public void test_empty_file() throws Exception {
+    Path p =
+        Paths.get(System.getProperty("user.dir"), "src", "test", "resources", "EmptyFile.java");
+    Result result =
+        new ImpSort(StandardCharsets.UTF_8, eclipseDefaults, true, true, LineEnding.AUTO)
+            .parseFile(p);
+    assertTrue(result.isSorted());
+  }
+
+  /**
+   * Test successfully parsing file without any newline.
+   */
+  @Test
+  public void test_file_without_newline() throws Exception {
+    Path p = Paths.get(System.getProperty("user.dir"), "src", "test", "resources",
+        "FileWithoutNewline.java");
+    Result result =
+        new ImpSort(StandardCharsets.UTF_8, eclipseDefaults, false, true, LineEnding.AUTO)
+            .parseFile(p);
+    assertTrue(result.isSorted());
+  }
+
+}

src/test/resources/FileWithoutNewline.java

@@ -0,0 +1 @@
+import java.lang.System;public class FileWithoutNewline{public static void main(String[] args){System.out.println("Hello, world!");}}