diff --git a/app/models/tag.rb b/app/models/tag.rb
index 1a3e3488d..b6e0a85b4 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -268,27 +268,29 @@ class Tag < ActiveRecord::Base
           case $1
           when "-user"
             q[:uploader_id_neg] ||= []
-            q[:uploader_id_neg] << User.name_to_id($2)
+            user_id = User.name_to_id($2)
+            q[:uploader_id_neg] << user_id unless user_id.blank?
 
           when "user"
             q[:uploader_id] = User.name_to_id($2)
-            q[:uploader_id] = -1 if q[:uploader_id].nil?
+            q[:uploader_id] = -1 if q[:uploader_id].blank?
 
           when "-approver"
             q[:approver_id_neg] ||= []
-            q[:approver_id_neg] << User.name_to_id($2)
+            user_id = User.name_to_id($2)
+            q[:approver_id_neg] << user_id unless user_id.blank?
 
           when "approver"
             q[:approver_id] = User.name_to_id($2)
-            q[:approver_id] = -1 if q[:approver_id].nil?
+            q[:approver_id] = -1 if q[:approver_id].blank?
 
           when "commenter", "comm"
             q[:commenter_id] = User.name_to_id($2)
-            q[:commenter_id] = -1 if q[:commenter_id].nil?
+            q[:commenter_id] = -1 if q[:commenter_id].blank?
 
           when "noter"
             q[:noter_id] = User.name_to_id($2)
-            q[:noter_id] = -1 if q[:noter_id].nil?
+            q[:noter_id] = -1 if q[:noter_id].blank?
 
           when "-pool"
             q[:tags][:exclude] << "pool:#{Pool.name_to_id($2)}"