fix: return serialized null value as string (#435)

Author: ivan-tymoshenko

index.js

@@ -94,7 +94,7 @@ class Serializer {
   }
 
   asIntegerNullable (i) {
-    return i === null ? null : this.asInteger(i)
+    return i === null ? 'null' : this.asInteger(i)
   }
 
   asNumber (i) {
@@ -107,15 +107,15 @@ class Serializer {
   }
 
   asNumberNullable (i) {
-    return i === null ? null : this.asNumber(i)
+    return i === null ? 'null' : this.asNumber(i)
   }
 
   asBoolean (bool) {
     return bool && 'true' || 'false' // eslint-disable-line
   }
 
   asBooleanNullable (bool) {
-    return bool === null ? null : this.asBoolean(bool)
+    return bool === null ? 'null' : this.asBoolean(bool)
   }
 
   asDatetime (date, skipQuotes) {
@@ -176,7 +176,7 @@ class Serializer {
   }
 
   asStringNullable (str) {
-    return str === null ? null : this.asString(str)
+    return str === null ? 'null' : this.asString(str)
   }
 
   // magically escape strings for json

test/nullable.test.js

@@ -116,3 +116,67 @@ Object.keys(testSet).forEach(key => {
     t.same(JSON.parse(result), expected)
   })
 })
+
+test('handle nullable number correctly', (t) => {
+  t.plan(2)
+
+  const schema = {
+    type: 'number',
+    nullable: true
+  }
+  const stringify = build(schema)
+
+  const data = null
+  const result = stringify(data)
+
+  t.same(result, JSON.stringify(data))
+  t.same(JSON.parse(result), data)
+})
+
+test('handle nullable integer correctly', (t) => {
+  t.plan(2)
+
+  const schema = {
+    type: 'integer',
+    nullable: true
+  }
+  const stringify = build(schema)
+
+  const data = null
+  const result = stringify(data)
+
+  t.same(result, JSON.stringify(data))
+  t.same(JSON.parse(result), data)
+})
+
+test('handle nullable boolean correctly', (t) => {
+  t.plan(2)
+
+  const schema = {
+    type: 'boolean',
+    nullable: true
+  }
+  const stringify = build(schema)
+
+  const data = null
+  const result = stringify(data)
+
+  t.same(result, JSON.stringify(data))
+  t.same(JSON.parse(result), data)
+})
+
+test('handle nullable string correctly', (t) => {
+  t.plan(2)
+
+  const schema = {
+    type: 'string',
+    nullable: true
+  }
+  const stringify = build(schema)
+
+  const data = null
+  const result = stringify(data)
+
+  t.same(result, JSON.stringify(data))
+  t.same(JSON.parse(result), data)
+})