🐛 (webhook) Fix variable list parsing in custom body

Closes #687

packages/lib/safeStringify.ts

@@ -0,0 +1,12 @@
+import { isNotDefined } from './utils'
+
+export const safeStringify = (val: unknown): string | null => {
+  if (isNotDefined(val)) return null
+  if (typeof val === 'string') return val
+  try {
+    return JSON.stringify(val)
+  } catch {
+    console.warn('Failed to safely stringify variable value', val)
+    return null
+  }
+}