Better support for null values (#130)

README.md

@@ -53,6 +53,7 @@ fast-json-stringify-uglified obj x 5,331,581 ops/sec ±0.73% (91 runs sampled)
  - <a href="#ref">`Reuse - $ref`</a>
  - <a href="#long">`Long integers`</a>
  - <a href="#uglify">`Uglify`</a>
+ - <a href="#nullable">`Nullable`</a>
 - <a href="#acknowledgements">`Acknowledgements`</a>
 - <a href="#license">`License`</a>
 
@@ -462,6 +463,35 @@ const stringify = fastJson({
 console.log(stringify({ some: 'object' })) // '{"some":"object"}'
 ```
 
+<a name="nullable"></a>
+#### Nullable
+
+According to the [Open API 3.0 specification](https://swagger.io/docs/specification/data-models/data-types/#null), a value that can be null must be declared `nullable`.
+
+##### Nullable object
+```javascript
+const stringify = fastJson({
+  'title': 'Nullable schema',
+  'type': 'object',
+  'nullable': true,
+  'properties': {
+    'product': {
+      'nullable': true,
+      'type': 'object',
+      'properties': {
+        'name': {
+          'type': 'string'
+        }
+      }
+    }
+  }
+})
+
+console.log(stringify({product: {name: "hello"}})) // "{"product":{"name":"hello"}}"
+console.log(stringify({product: null})) // "{"product":null}"
+console.log(stringify(null)) // null
+```
+
 <a name="acknowledgements"></a>
 ## Acknowledgements
 

index.js

@@ -621,6 +621,15 @@ function toJSON (variableName) {
 function buildObject (schema, code, name, externalSchema, fullSchema) {
   code += `
     function ${name} (input) {
+  `
+  if (schema.nullable) {
+    code += `
+      if(input === null) {
+        return '${$asNull()}';
+      }
+  `
+  }
+  code += `
       var obj = ${toJSON('input')}
       var json = '{'
       var addComma = false

test/toJSON.test.js

@@ -81,3 +81,94 @@ test('not use toJSON if does not exist', (t) => {
 
   t.equal('{"product":{"name":"cola"}}', stringify(object))
 })
+
+test('not fail on null object declared nullable', (t) => {
+  t.plan(1)
+
+  const stringify = build({
+    title: 'simple object',
+    type: 'object',
+    nullable: true,
+    properties: {
+      product: {
+        type: 'object',
+        properties: {
+          name: {
+            type: 'string'
+          }
+        }
+      }
+    }
+  })
+  t.equal('null', stringify(null))
+})
+
+test('not fail on null sub-object declared nullable', (t) => {
+  t.plan(1)
+
+  const stringify = build({
+    title: 'simple object',
+    type: 'object',
+    properties: {
+      product: {
+        nullable: true,
+        type: 'object',
+        properties: {
+          name: {
+            type: 'string'
+          }
+        }
+      }
+    }
+  })
+  const object = {
+    product: null
+  }
+  t.equal('{"product":null}', stringify(object))
+})
+
+test('throw an error on non nullable null sub-object', (t) => {
+  t.plan(1)
+
+  const stringify = build({
+    title: 'simple object',
+    type: 'object',
+    properties: {
+      product: {
+        nullable: false,
+        type: 'object',
+        properties: {
+          name: {
+            type: 'string'
+          }
+        }
+      }
+    }
+  })
+  const object = {
+    product: null
+  }
+  t.throws(() => { stringify(object) })
+})
+
+test('throw an error on non nullable null object', (t) => {
+  t.plan(1)
+
+  const stringify = build({
+    title: 'simple object',
+    nullable: false,
+    type: 'object',
+    properties: {
+      product: {
+        nullable: false,
+        type: 'object',
+        properties: {
+          name: {
+            type: 'string'
+          }
+        }
+      }
+    }
+  })
+  t.throws(() => { stringify(null) })
+})