feat(vault): review suggestions

Signed-off-by: Sascha Isele <s.isele@cluetec.de>

extensions/common/vault/vault-hashicorp/src/main/java/org/eclipse/edc/vault/hashicorp/HashicorpVaultExtension.java

@@ -71,7 +71,7 @@ public class HashicorpVaultExtension implements ServiceExtension {
     @Setting(value = "The URL path of the vault's /secret endpoint", defaultValue = VAULT_API_SECRET_PATH_DEFAULT)
     public static final String VAULT_API_SECRET_PATH = "edc.vault.hashicorp.api.secret.path";
 
-    @Setting(value = "The path of the folder that the secret is stored in", required = false, defaultValue = "")
+    @Setting(value = "The path of the folder that the secret is stored in, relative to VAULT_FOLDER_PATH")
     public static final String VAULT_FOLDER_PATH = "edc.vault.hashicorp.folder";
 
     @Inject
@@ -147,7 +147,7 @@ private HashicorpVaultSettings getSettings(ServiceExtensionContext context) {
         var ttl = context.getSetting(VAULT_TOKEN_TTL, VAULT_TOKEN_TTL_DEFAULT);
         var renewBuffer = context.getSetting(VAULT_TOKEN_RENEW_BUFFER, VAULT_TOKEN_RENEW_BUFFER_DEFAULT);
         var secretPath = context.getSetting(VAULT_API_SECRET_PATH, VAULT_API_SECRET_PATH_DEFAULT);
-        var folderPath = context.getSetting(VAULT_FOLDER_PATH, "");
+        var folderPath = context.getSetting(VAULT_FOLDER_PATH, null);
 
         return HashicorpVaultSettings.Builder.newInstance()
                 .url(url)