diff --git a/src/Logic/Tags/ComparingTag.ts b/src/Logic/Tags/ComparingTag.ts
index 981a64a92e..56da517ee0 100644
--- a/src/Logic/Tags/ComparingTag.ts
+++ b/src/Logic/Tags/ComparingTag.ts
@@ -1,6 +1,7 @@
 import { TagsFilter } from "./TagsFilter"
 import { TagConfigJson } from "../../Models/ThemeConfig/Json/TagConfigJson"
 import { Tag } from "./Tag"
+import { ExpressionSpecification } from "maplibre-gl"
 
 export default class ComparingTag implements TagsFilter {
     private readonly _key: string
@@ -12,7 +13,7 @@ export default class ComparingTag implements TagsFilter {
         key: string,
         predicate: (value: string | undefined) => boolean,
         representation: "<" | ">" | "<=" | ">=",
-        boundary: string
+        boundary: string,
     ) {
         this._key = key
         this._predicate = predicate
@@ -125,4 +126,8 @@ export default class ComparingTag implements TagsFilter {
     visit(f: (TagsFilter) => void) {
         f(this)
     }
+
+    asMapboxExpression(): ExpressionSpecification {
+        return [this._representation, ["get", this._key], this._boundary]
+    }
 }
diff --git a/src/Logic/Tags/SubstitutingTag.ts b/src/Logic/Tags/SubstitutingTag.ts
index 6e9d293116..bf13dc7c35 100644
--- a/src/Logic/Tags/SubstitutingTag.ts
+++ b/src/Logic/Tags/SubstitutingTag.ts
@@ -2,6 +2,7 @@ import { TagsFilter } from "./TagsFilter"
 import { Tag } from "./Tag"
 import { Utils } from "../../Utils"
 import { TagConfigJson } from "../../Models/ThemeConfig/Json/TagConfigJson"
+import { ExpressionSpecification } from "maplibre-gl"
 
 /**
  * The substituting-tag uses the tags of a feature a variables and replaces them.
@@ -23,6 +24,10 @@ export default class SubstitutingTag implements TagsFilter {
         this._invert = invert
     }
 
+    asMapboxExpression(): ExpressionSpecification {
+        throw new Error("Method not implemented.")
+    }
+
     private static substituteString(template: string, dict: Record<string, string>): string {
         for (const k in dict) {
             template = template.replace(new RegExp("\\{" + k + "\\}", "g"), dict[k])
diff --git a/src/UI/Popup/TagRendering/TagRenderingQuestion.svelte b/src/UI/Popup/TagRendering/TagRenderingQuestion.svelte
index ae33fc1bab..0bdce9a730 100644
--- a/src/UI/Popup/TagRendering/TagRenderingQuestion.svelte
+++ b/src/UI/Popup/TagRendering/TagRenderingQuestion.svelte
@@ -153,7 +153,7 @@
     }
   })
   $: {
-    if (allowDeleteOfFreeform && $freeformInput === undefined && $freeformInputUnvalidated === "" && mappings?.length === 0) {
+    if (allowDeleteOfFreeform && $freeformInput === undefined && $freeformInputUnvalidated === "" && (mappings?.length ?? 0) === 0) {
       selectedTags = new Tag(config.freeform.key, "")
     } else {
 
@@ -394,7 +394,7 @@
             <!-- TagRenderingQuestion-buttons -->
             <slot name="cancel" />
             <slot name="save-button" {selectedTags}>
-              {#if allowDeleteOfFreeform && mappings?.length === 0 && $freeformInput === undefined && $freeformInputUnvalidated === ""}
+              {#if allowDeleteOfFreeform && (mappings?.length ?? 0) === 0 && $freeformInput === undefined && $freeformInputUnvalidated === ""}
                 <button class="primary flex" on:click|stopPropagation|preventDefault={onSave}>
                   <TrashIcon class="w-6 h-6 text-red-500" />
                   <Tr t={Translations.t.general.eraseValue}/>