[MRAR-80] Bump junit from 4.12 to 4.13

Bumps [junit](https://github.com/junit-team/junit4) from 4.12 to 4.13.
- [Release notes](https://github.com/junit-team/junit4/releases)
- [Changelog](https://github.com/junit-team/junit4/blob/master/doc/ReleaseNotes4.12.md)
- [Commits](https://github.com/junit-team/junit4/compare/r4.12...r4.13)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
diff --git a/pom.xml b/pom.xml
index cc03ea1..bfb52a8 100644
--- a/pom.xml
+++ b/pom.xml
@@ -131,7 +131,7 @@
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
-      <version>4.12</version>
+      <version>4.13</version>
       <scope>test</scope>
     </dependency>
     <dependency>
diff --git a/src/test/java/org/apache/maven/plugins/rar/RarMojoTest.java b/src/test/java/org/apache/maven/plugins/rar/RarMojoTest.java
index f66fda6..838c34c 100644
--- a/src/test/java/org/apache/maven/plugins/rar/RarMojoTest.java
+++ b/src/test/java/org/apache/maven/plugins/rar/RarMojoTest.java
@@ -23,6 +23,7 @@
 import java.util.ArrayList;
 import java.util.Enumeration;
 import java.util.List;
+import java.util.Objects;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 
@@ -80,6 +81,7 @@
         assertTrue( workDirectory.isDirectory() );
 
         File[] fileNames = workDirectory.listFiles();
+        assertNotNull( fileNames );
 
         List<String> expectedFiles = new ArrayList<String>();
 
@@ -164,6 +166,7 @@
         assertTrue( workDirectory.isDirectory() );
 
         File[] fileNames = workDirectory.listFiles();
+        assertNotNull( fileNames );
 
         List<String> expectedFiles = new ArrayList<String>();
         List<String> fileList = new ArrayList<String>();
@@ -238,6 +241,7 @@
         assertTrue( workDirectory.isDirectory() );
 
         File[] fileNames = workDirectory.listFiles();
+        assertNotNull( fileNames );
 
         List<String> expectedFiles = new ArrayList<String>();
         List<String> fileList = new ArrayList<String>();
@@ -337,7 +341,7 @@
 
             File[] files = file.listFiles();
 
-            for (File file1 : files) {
+            for (File file1 : Objects.requireNonNull( files ) ) {
                 addFileToList(file1, fileList);
             }
         }