[core] Port rjsf-team/react-jsonschema-form#4745

Author: x0k

.changeset/plenty-crabs-do.md

@@ -0,0 +1,5 @@
+---
+"@sjsf/form": patch
+---
+
+Port https://github.com/rjsf-team/react-jsonschema-form/pull/4745

packages/form/src/core/default-state.test.ts

@@ -6281,4 +6281,20 @@ describe("getDefaultFormState2()", () => {
       )
     ).toEqual({ stringArray: [undefined], numberArray: [] });
   });
+  it("handles a `null` default value", () => {
+    const schema: Schema = {
+      type: "object",
+      properties: {
+        empty: {
+          type: "null",
+          default: null,
+        },
+      },
+    };
+    expect(
+      getDefaultFormState(testValidator, defaultMerger, schema, {}, schema)
+    ).toEqual({
+      empty: null,
+    });
+  });
 });

packages/form/src/core/merge.test.ts

@@ -484,6 +484,20 @@ describe("mergeDefaultsWithFormData()", () => {
     expect(mergeDefaultsWithFormData({}, null, undefined, true)).toEqual({});
   });
 
+  it("should return null if default is null and formData is undefined and defaultSupercedesUndefined is true", () => {
+    const defaultValue = null;
+    const formData = undefined;
+    const defaultSupercedesUndefined = true;
+    expect(
+      mergeDefaultsWithFormData(
+        defaultValue,
+        formData,
+        undefined,
+        defaultSupercedesUndefined
+      )
+    ).toBeNull();
+  });
+
   it("should return undefined when formData is undefined", () => {
     expect(mergeDefaultsWithFormData(undefined, undefined)).toBeUndefined();
   });

packages/form/src/core/merge.ts

@@ -239,7 +239,7 @@ export function mergeDefaultsWithFormData<T = any>(
 
   if (
     (defaultsSupersedesUndefined &&
-      ((!isNil(defaults) && isNil(formData)) ||
+      ((!(defaults === undefined) && isNil(formData)) ||
         (typeof formData === "number" && isNaN(formData)))) ||
     (overrideFormDataWithDefaults && !isNil(formData))
     // NOTE: The above condition is inherited from RJSF to maintain tests compatibility
@@ -255,7 +255,7 @@ export function mergeDefaultsWithFormData<T = any>(
 
 export function mergeSchemaObjects<
   A extends SchemaObjectValue,
-  B extends SchemaObjectValue
+  B extends SchemaObjectValue,
 >(obj1: A, obj2: B, concatArrays: boolean | "preventDuplicates" = false) {
   const acc: SchemaObjectValue = Object.assign({}, obj1);
   for (const [key, right] of Object.entries(obj2)) {