handle null attributes in getSearchDescription()

fixes #3360

Author: Vladimir Kotal

plugins/src/main/java/opengrok/auth/plugin/ldap/LdapFacade.java

@@ -307,8 +307,18 @@ private <T> LdapSearchResult<T> lookup(String dn, String filter, String[] attrib
         return res;
     }
 
-    private String getSearchDescription(String dn, String filter, String[] attributes) {
-        return "DN: " + dn + " , filter: " + filter + " , attributes: " + String.join(",", attributes);
+    // available for testing
+    static String getSearchDescription(String dn, String filter, String[] attributes) {
+        StringBuilder builder = new StringBuilder();
+        builder.append("DN: ");
+        builder.append(dn);
+        builder.append(" , filter: ");
+        builder.append(filter);
+        if (attributes != null) {
+            builder.append(" , attributes: ");
+            builder.append(String.join(",", attributes));
+        }
+        return builder.toString();
     }
 
     /**

plugins/src/test/java/opengrok/auth/plugin/ldap/LdapFacadeTest.java

@@ -131,4 +131,12 @@ public void testPrepareServersNegative() throws UnknownHostException {
         facade.prepareServers();
         assertFalse(facade.isConfigured());
     }
+
+    @Test
+    public void testGetSearchDescription() {
+        assertEquals("DN: foo , filter: bar , attributes: Bilbo,Frodo",
+                LdapFacade.getSearchDescription("foo", "bar", new String[]{"Bilbo", "Frodo"}));
+        assertEquals("DN: foo , filter: bar",
+                LdapFacade.getSearchDescription("foo", "bar", null));
+    }
 }