fix: omit nulls

src/Data/YAML/Foreign/Encode.js

@@ -13,6 +13,15 @@ export function objToHash(valueToYAMLImpl, fst, snd, obj) {
 }
 
 export function toYAMLImpl(a) {
-  // noCompatMode does not support YAML 1.1
-  return yaml.dump(a, { noCompatMode: true })
+  const replacer = (_, v) => {
+    if (typeof v === 'object') {
+      Object.keys(v).forEach(k => {
+        if (v[k] === null) {
+          delete v[k]
+        }
+      })
+    }
+  }
+
+  return yaml.dump(a, { noCompatMode: true, replacer })
 }