fix(core): mergeDeep now can merge nulls (#4088)

packages/core/src/utilities/mergeDeep.ts

@@ -5,14 +5,10 @@ export function mergeDeep(target: Record<string, any>, source: Record<string, an
 
   if (isPlainObject(target) && isPlainObject(source)) {
     Object.keys(source).forEach(key => {
-      if (isPlainObject(source[key])) {
+      if (isPlainObject(source[key]) && isPlainObject(target[key])) {
-        if (!(key in target)) {
+        output[key] = mergeDeep(target[key], source[key])
-          Object.assign(output, { [key]: source[key] })
-        } else {
-          output[key] = mergeDeep(target[key], source[key])
-        }
       } else {
-        Object.assign(output, { [key]: source[key] })
+        output[key] = source[key]
       }
     })
   }

tests/cypress/integration/core/mergeDeep.spec.ts

@@ -19,6 +19,21 @@ describe('mergeDeep', () => {
     expect(merged).to.deep.eq(result)
   })
 
+  it('should merge when source has null value', () => {
+    const one = {
+      a: null,
+    }
+    const two = {
+      a: { c: 3 },
+    }
+    const result = {
+      a: { c: 3 },
+    }
+    const merged = mergeDeep(one, two)
+
+    expect(merged).to.deep.eq(result)
+  })
+
   it('should not merge array', () => {
     const one = {
       a: [1],
@@ -34,6 +49,36 @@ describe('mergeDeep', () => {
     expect(merged).to.deep.eq(result)
   })
 
+  it('should merge when source has null value', () => {
+    const one = {
+      a: null,
+    }
+    const two = {
+      a: { c: 3 },
+    }
+    const result = {
+      a: { c: 3 },
+    }
+    const merged = mergeDeep(one, two)
+
+    expect(merged).to.deep.eq(result)
+  })
+
+  it('should allow nulling a value', () => {
+    const one = {
+      a: { c: 3 },
+    }
+    const two = {
+      a: { c: null },
+    }
+    const result = {
+      a: { c: null },
+    }
+    const merged = mergeDeep(one, two)
+
+    expect(merged).to.deep.eq(result)
+  })
+
   it('should merge deep', () => {
     const one = {
       a: 1,