Strip null values for changelog and set size limit for large content blocks

web-app/src/lib/components/MarkdownEditor.svelte

@@ -63,6 +63,7 @@
   <textarea
     {name}
     rows="20"
+    maxlength="200000"
     bind:value={previewContent.value}
     bind:this={mainContentTextarea}
     onscroll={updateScrollPercentage}