diff --git a/api/api.py b/api/api.py
index e34086c..47a452f 100644
--- a/api/api.py
+++ b/api/api.py
@@ -212,7 +212,7 @@ def make_filter_query(filter):
             else:
                 parameter = sql.SQL("CAST({parameter} AS {cast})").format(parameter=parameter, cast=sql.SQL(subfilter['cast']))
 
-        if 'value' not in subfilter or subfilter['value'] == '':
+        if subfilter['comparison'] == 'is null' or subfilter['comparison'] == 'is not null':
             filter_query = sql.SQL("{filter_query} ({parameter} {comparison})").format(filter_query=filter_query, parameter=parameter, comparison=sql.SQL(subfilter['comparison']))
         else:
             if subfilter['comparison'] == 'starts with':
diff --git a/frontend/src/components/FeatureCustom.vue b/frontend/src/components/FeatureCustom.vue
index 8d19bfe..2434623 100644
--- a/frontend/src/components/FeatureCustom.vue
+++ b/frontend/src/components/FeatureCustom.vue
@@ -24,8 +24,21 @@
             v-model="f.parameter"
             :items="$store.state.osmKeys"
             @input="getValues"
-          ></v-combobox
-        ></v-col>
+          >
+            <template
+              v-slot:append
+              v-if="f.parameter != '' && f.parameter != null"
+            >
+              <a
+                :href="'https://wiki.openstreetmap.org/wiki/Key:' + f.parameter"
+                target="_blank"
+                class="super"
+              >
+                <v-icon x-small>mdi-open-in-new</v-icon></a
+              >
+            </template>
+          </v-combobox></v-col
+        >
         <v-col>
           <!-- Dropdown for type of comparison between parameter and value -->
           <v-select
@@ -63,7 +76,12 @@
     </v-card-text>
     <v-card-actions>
       <v-btn color="secondary" text @click="addFilter">Add condition</v-btn>
-      <v-btn style="margin-left: auto" color="primary" text @click="addCustom"
+      <v-btn
+        style="margin-left: auto"
+        color="primary"
+        text
+        @click="addCustom"
+        :disabled="filters[0].parameter == ''"
         >Add custom feature</v-btn
       >
     </v-card-actions>
diff --git a/frontend/src/components/SearchResult.vue b/frontend/src/components/SearchResult.vue
index 3db35e4..03c7340 100644
--- a/frontend/src/components/SearchResult.vue
+++ b/frontend/src/components/SearchResult.vue
@@ -25,18 +25,12 @@
         </div>
       </v-card-text>
       <v-card-actions>
-        <!-- <a
-          class="outlink"
-          target="_blank"
-          :href="`https://www.google.com/maps/search/?api=1&query=${result.lat},${result.lng}`"
-        > -->
         <v-btn
           :href="`https://www.google.com/maps/search/?api=1&query=${result.lat},${result.lng}`"
           text
           target="_blank"
           >({{ result.lat.toFixed(5) }}, {{ result.lng.toFixed(5) }})</v-btn
         >
-        <!-- </a> -->
       </v-card-actions>
     </v-card>
   </v-col>