fix: removing last zone was not reflected in full data

This changes the behavior of saving metadata so that an empty
zones array resulting from removing the last, previously added
zone, will be handled as null value. The code handling full
model deals properly with nulls, while empty arrays are
silently ignored as updates.

packages/server-admin-ui/src/views/DataBrowser/Meta.js

@@ -338,7 +338,7 @@ export default function Meta({ meta, path }) {
           />
         )}
         <Zones
-          zones={zones}
+          zones={zones !== undefined && zones !== null ? zones : []}
           isEditing={isEditing}
           setZones={(zones) => setLocalMeta({ ...localMeta, zones })}
         ></Zones>

src/put.js

@@ -108,6 +108,13 @@ module.exports = {
         metaPath = parts.slice(0, parts.length - 1).join('.')
       }
 
+      // set empty zones array explicitly to null
+      for (const prop in metaValue) {
+        if (Array.isArray(metaValue[prop]) && metaValue[prop].length === 0) {
+          metaValue[prop] = null
+        }
+      }
+
       app.config.baseDeltaEditor.setMeta(context, metaPath, metaValue)
 
       let full_meta = getMetadata('vessels.self.' + metaPath)