SLING-4234 : Tenant create implementation does not match with the API 

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1722867 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/main/java/org/apache/sling/tenant/TenantManager.java b/src/main/java/org/apache/sling/tenant/TenantManager.java
index 63f3a07..94d5b55 100644
--- a/src/main/java/org/apache/sling/tenant/TenantManager.java
+++ b/src/main/java/org/apache/sling/tenant/TenantManager.java
@@ -60,10 +60,9 @@
      *            though, that this map contain at least the
      *            {@link Tenant#PROP_NAME} and {@link Tenant#PROP_DESCRIPTION}
      *            properties.
-     * @return The newly created {@link Tenant} instance.
+     * @return The newly created {@link Tenant} instance or {@code null} if a tenant
+     *         with the id already exists.
      * @throws NullPointerException if {@code tenantId} is {@code null}.
-     * @throws IllegalArgumentException if a tenant with the same
-     *             {@code tentantId} already exists.
      */
     Tenant create(String tenantId, Map<String, Object> properties);