Fix minor checkstyle issues

- Add JavaDoc where checkstyle expects it
- Fix line too long issues
- ...

src/main/java/fr/xephi/authme/command/executable/HelpCommand.java

@@ -20,6 +20,9 @@ import static fr.xephi.authme.command.help.HelpProvider.SHOW_CHILDREN;
 import static fr.xephi.authme.command.help.HelpProvider.SHOW_COMMAND;
 import static fr.xephi.authme.command.help.HelpProvider.SHOW_DESCRIPTION;
 
+/**
+ * Displays help information to a user.
+ */
 public class HelpCommand implements ExecutableCommand {
 
     @Inject
@@ -51,7 +54,8 @@ public class HelpCommand implements ExecutableCommand {
 
         int mappedCommandLevel = result.getCommandDescription().getLabelCount();
         if (mappedCommandLevel == 1) {
-            helpProvider.outputHelp(sender, result, SHOW_COMMAND | SHOW_DESCRIPTION | SHOW_CHILDREN | SHOW_ALTERNATIVES);
+            helpProvider.outputHelp(sender, result,
+                SHOW_COMMAND | SHOW_DESCRIPTION | SHOW_CHILDREN | SHOW_ALTERNATIVES);
         } else {
             helpProvider.outputHelp(sender, result, ALL_OPTIONS);
         }

src/main/java/fr/xephi/authme/command/executable/authme/debug/TestEmailSender.java

@@ -68,6 +68,17 @@ class TestEmailSender implements DebugSection {
         return DebugSectionPermissions.TEST_EMAIL;
     }
 
+    /**
+     * Gets the email address to use based on the sender and the arguments. If the arguments are empty,
+     * we attempt to retrieve the email from the sender. If there is an argument, we verify that it is
+     * an email address.
+     * {@code null} is returned if no email address could be found. This method informs the sender of
+     * the specific error in such cases.
+     *
+     * @param sender the command sender
+     * @param arguments the provided arguments
+     * @return the email to use, or null if none found
+     */
     private String getEmail(CommandSender sender, List<String> arguments) {
         if (arguments.isEmpty()) {
             DataSourceResult<String> emailResult = dataSource.getEmail(sender.getName());

src/main/java/fr/xephi/authme/command/executable/register/RegisterCommand.java

@@ -97,6 +97,15 @@ public class RegisterCommand extends PlayerCommand {
         return null;
     }
 
+    /**
+     * Verifies that the second argument is valid (based on the configuration)
+     * to perform a password registration. The player is informed if the check
+     * is unsuccessful.
+     *
+     * @param player the player to register
+     * @param arguments the provided arguments
+     * @return true if valid, false otherwise
+     */
     private boolean isSecondArgValidForPasswordRegistration(Player player, List<String> arguments) {
         RegisterSecondaryArgument secondArgType = commonService.getProperty(REGISTER_SECOND_ARGUMENT);
         // cases where args.size < 2
@@ -143,6 +152,15 @@ public class RegisterCommand extends PlayerCommand {
         }
     }
 
+    /**
+     * Verifies that the second argument is valid (based on the configuration)
+     * to perform an email registration. The player is informed if the check
+     * is unsuccessful.
+     *
+     * @param player the player to register
+     * @param arguments the provided arguments
+     * @return true if valid, false otherwise
+     */
     private boolean isSecondArgValidForEmailRegistration(Player player, List<String> arguments) {
         RegisterSecondaryArgument secondArgType = commonService.getProperty(REGISTER_SECOND_ARGUMENT);
         // cases where args.size < 2