isExistを引数なしでも実行できるように

source/src/main/java/one/nem/lacerta/source/file/FileManager.java

@@ -16,6 +16,7 @@ public interface FileManager {
 
     File getFileRef();
     boolean isExist(String name) throws IOException;
+    boolean isExist() throws IOException;
     boolean isDirectory();
     boolean isFile();
     boolean isWritable();

source/src/main/java/one/nem/lacerta/source/file/impl/FileManagerImpl.java

@@ -76,6 +76,11 @@ public class FileManagerImpl implements FileManager {
         return Files.exists(resolvedPath);
     }
 
+    @Override
+    public boolean isExist() throws IOException {
+        return Files.exists(this.path);
+    }
+
     @Override
     public boolean isDirectory() {
         if (this.isExist()) {