Fix possible NPE

Fixes #347

src/main/java/the/bytecode/club/bytecodeviewer/resources/importing/impl/APKResourceImporter.java

@@ -56,7 +56,7 @@ public class APKResourceImporter implements Importer
 			container.resourceFiles = JarUtils.loadResources(decodedResources);
 		}
 		
-		Objects.requireNonNull(container.resourceFiles).putAll(JarUtils.loadResources(tempCopy)); //copy and rename
+		container.resourceFiles.putAll(JarUtils.loadResources(tempCopy)); // copy and rename
 		// to prevent unicode filenames
 		
 		String name = MiscUtils.getRandomizedName() + ".jar";

src/main/java/the/bytecode/club/bytecodeviewer/util/JarUtils.java

@@ -201,7 +201,7 @@ public class JarUtils
      */
     public static Map<String, byte[]> loadResources(final File zipFile) throws IOException {
         if (!zipFile.exists())
-            return null; //just ignore
+            return new LinkedHashMap<>(); // just ignore (don't return null for null-safety!)
     
         Map<String, byte[]> files = new LinkedHashMap<>();