Adds info about the encrypt and decrypt signs, and fixes a bug in group decryption

README.md

@@ -37,3 +37,14 @@ The **_give_** sign must have **[Give]** on its second line.
 The third and fourth line contains the book to be loaded.
 This can either be a numerical id pointing to a publicly saved book,
 or the full text identifier of the book (book name, author).
+
+#### Encrypt sign
+
+The **_encrypt_** sign must have **[Encrypt]** on its second line.
+The third line must contain the encryption key
+The fourth line can be empty or contain "dna" for dna-based encryption.
+
+#### Decrypt sign
+
+The **_decrypt_** sign must have **[Decrypt]** on its second line.
+The third line must contain the decryption key

src/main/java/net/knarcraft/bookswithoutborders/BooksWithoutBorders.java

@@ -388,7 +388,7 @@ public class BooksWithoutBorders extends JavaPlugin {
             file = FileHelper.getBookFile(getBookFolder() + fileName);
         } else if (dir.equalsIgnoreCase("player")) {
             file = FileHelper.getBookFile(getBookFolder() + cleanString(sender.getName()) + getSlash() + fileName);
-        } else if (dir.trim().isEmpty()) {
+        } else if (!dir.trim().isEmpty()) {
             file = FileHelper.getBookFile(getBookFolder() + "Encrypted" + getSlash() + dir + getSlash() + fileName);
         } else {
             file = null;

src/main/java/net/knarcraft/bookswithoutborders/listener/SignEventListener.java

@@ -254,6 +254,10 @@ public class SignEventListener implements Listener {
         }
         newBook = BooksWithoutBorders.getInstance().loadBook(player, fileName, "true", groupName, heldItem.getAmount());
 
+        if (newBook == null) {
+            return;
+        }
+
         player.getInventory().setItem(hand, newBook);
         player.closeInventory();
         player.sendMessage(ChatColor.GREEN + "Book auto-decrypted!");