fix(core): evaluate nested exists false filter when parent key is nullish (#5017)

Signed-off-by: Gaurav Patil <gauravpatil2516@gmail.com>

Author: GauravPatil2515

packages/core/src/eventFilterMatches.ts

@@ -5,16 +5,10 @@ import type { EventFilter } from "./schemas/eventFilter.js";
 // If the values of the array are objects, then we are doing content filtering
 // An example would be [{ $endsWith: ".png" }, { $startsWith: "images/" } ]
 export function eventFilterMatches(payload: any, filter: EventFilter): boolean {
-  if (payload === undefined || payload === null) {
-    if (Object.entries(filter).length === 0) {
-      return true;
-    } else {
-      return false;
-    }
-  }
+  const safePayload = payload ?? {};
 
   for (const [patternKey, patternValue] of Object.entries(filter)) {
-    const payloadValue = payload[patternKey];
+    const payloadValue = safePayload[patternKey];
 
     if (Array.isArray(patternValue)) {
       if (patternValue.length === 0) {

packages/core/test/eventFilterMatches.test.ts

@@ -209,6 +209,20 @@ describe("eventFilterMatches", () => {
     expect(eventFilterMatches(payload, filter)).toBe(true);
   });
 
+  it("should return true for nested $exists: false when parent key is missing or null", () => {
+    const filter: EventFilter = {
+      user: {
+        email: [{ $exists: false }],
+      },
+    };
+
+    expect(eventFilterMatches({}, filter)).toBe(true);
+    expect(eventFilterMatches({ user: null }, filter)).toBe(true);
+    expect(eventFilterMatches({ user: {} }, filter)).toBe(true);
+    expect(eventFilterMatches({ user: { email: undefined } }, filter)).toBe(true);
+    expect(eventFilterMatches({ user: { email: "user@example.com" } }, filter)).toBe(false);
+  });
+
   it("should return true when payload does match numeric condition", () => {
     const payload = {
       name: "John",