fix: Set falsy values as default to schema fields (parse-community#5868)

Author: alencarlucas

spec/schemas.spec.js

@@ -425,6 +425,8 @@ describe('schemas', () => {
           foo4: { type: 'Date', required: true },
           foo5: { type: 'Number', defaultValue: 5 },
           ptr: { type: 'Pointer', targetClass: 'SomeClass', required: false },
+          defaultFalse: { type: 'Boolean', required: true, defaultValue: false },
+          defaultZero: { type: 'Number', defaultValue: 0 }
         },
       },
     }).then(async response => {
@@ -445,6 +447,8 @@ describe('schemas', () => {
           foo4: { type: 'Date', required: true },
           foo5: { type: 'Number', defaultValue: 5 },
           ptr: { type: 'Pointer', targetClass: 'SomeClass', required: false },
+          defaultFalse: { type: 'Boolean', required: true, defaultValue: false },
+          defaultZero: { type: 'Number', defaultValue: 0 }
         },
         classLevelPermissions: defaultClassLevelPermissions,
       });
@@ -464,6 +468,9 @@ describe('schemas', () => {
       expect(obj.get('foo4')).toEqual(date);
       expect(obj.get('foo5')).toEqual(5);
       expect(obj.get('ptr')).toBeUndefined();
+      expect(obj.get('defaultFalse')).toEqual(false)
+      expect(obj.get('defaultZero')).toEqual(0)
+      expect(obj.get('ptr')).toBeUndefined();
       done();
     });
   });

src/RestWrite.js

@@ -338,7 +338,8 @@ RestWrite.prototype.setRequiredFieldsIfNeeded = function() {
           if (
             setDefault &&
             schema.fields[fieldName] &&
-            schema.fields[fieldName].defaultValue &&
+            schema.fields[fieldName].defaultValue !== null &&
+            schema.fields[fieldName].defaultValue !== undefined &&
             (this.data[fieldName] === undefined ||
               (typeof this.data[fieldName] === 'object' &&
                 this.data[fieldName].__op === 'Delete'))