handle a scene merge edge case where null values would cause the diff…

… to crash

source/server/utils/merge/diff.test.ts

@@ -83,11 +83,19 @@ describe("merge.diff()", function(){
     it("throws when diffing an array with an object", function(){
       expect(()=>diff({a:[]}, {a:{}})).to.throw("Can't diff an array with an object");
     });
+
+    it("handles null in arrays", function(){
+      expect(diff({a:[0, null, 0]}, {a:[0,0, null]})).to.deep.equal({a:{1:0, 2:null}});
+    });
   });
 
   describe("objects", function(){
     it("deep merge objects", function(){
       expect(diff<any>({v: {a: 1 }}, {v: {a:1, b:2}})).to.deep.equal({v:{b:2}});
     });
+
+    it("handles object creation", function(){
+      expect(diff({name:"A", articles: null}, {name:"A", articles: {id:"1"}})).to.deep.equal({articles: {id:"1"}});
+    })
   });
 });

source/server/utils/merge/diff.ts

@@ -38,6 +38,12 @@ export default function diff<T extends Record<string,any>>(from :T, to :T) :Diff
       continue;
     }
 
+    if(from[key] == null){
+      //We already verified that to[key] is not null
+      r[key] = to[key];
+      continue;
+    }
+
     const d = diff(from[key] as any, to[key] as any);
     if(Object.keys(d).length){
       //console.log("Diffing", key, from[key], to[key]);