Updated FAQ (markdown)

FAQ.md

@@ -17,6 +17,7 @@
   - [Why does the generated JSON contain garbage?](#why-does-the-generated-json-contain-garbage)
   - [How to compute the JSON length?](#how-to-compute-the-json-length)
   - [How to create complex nested objects?](#how-to-create-complex-nested-objects)
+  - [How to insert a `null`?](#how-to-insert-a-null)
   - [The first serialization succeeds, why do the next ones fail?](#the-first-serialization-succeeds-why-do-the-next-ones-fail)
   - [Why ArduinoJson is slow?](#why-arduinojson-is-slow)
 - [Part 3 - Deserialization/parsing questions](#part-3---deserializationparsing-questions)
@@ -24,6 +25,11 @@
   - [Can I parse data from a stream?](#can-i-parse-data-from-a-stream)
   - [Can I parse a JSON input that is too big to fit in memory?](#can-i-parse-a-json-input-that-is-too-big-to-fit-in-memory)
   - [Why parsing fails?](#why-parsing-fails)
+    - [Case 1: The input is not a valid JSON](#case-1-the-input-is-not-a-valid-json)
+    - [Case 2: The `StaticJsonBuffer` is too small](#case-2-the-staticjsonbuffer-is-too-small)
+    - [Case 3: The `StaticJsonBuffer` is too big](#case-3-the-staticjsonbuffer-is-too-big)
+    - [Case 4: The `DynamicJsonBuffer` fails to allocate memory](#case-4-the-dynamicjsonbuffer-fails-to-allocate-memory)
+    - [Case 5: You called `parseObject\(\)` instead of `parseArray\(\)`](#case-5-you-called-parseobject-instead-of-parsearray)
   - [The first parsing succeeds, why do the next ones fail?](#the-first-parsing-succeeds-why-do-the-next-ones-fail)
   - [Parsing succeeds but I can't read the values!](#parsing-succeeds-but-i-cant-read-the-values)
   - [How to know the type of a value?](#how-to-know-the-type-of-a-value)
@@ -448,7 +454,41 @@ will generate:
 }
 ```
 
-See issues [#51](https://github.com/bblanchon/ArduinoJson/issues/51), [#252](https://github.com/bblanchon/ArduinoJson/issues/252) and [#264](https://github.com/bblanchon/ArduinoJson/issues/264)
+See:
+
+* issues [#51](https://github.com/bblanchon/ArduinoJson/issues/51), [#252](https://github.com/bblanchon/ArduinoJson/issues/252) and [#264](https://github.com/bblanchon/ArduinoJson/issues/264)
+* [API Reference: JsonArray::createNestedArray()](https://github.com/bblanchon/ArduinoJson/wiki/API-Reference#jsonarraycreatenestedarray)
+* [API Reference: JsonArray::createNestedArray()](https://github.com/bblanchon/ArduinoJson/wiki/API-Reference#jsonarraycreatenestedarray)
+* [API Reference: JsonObject::createNestedArray()](https://github.com/bblanchon/ArduinoJson/wiki/API-Reference#jsonobjectcreatenestedarray)
+* [API Reference: JsonObject::createNestedObject()](https://github.com/bblanchon/ArduinoJson/wiki/API-Reference#jsonobjectcreatenestedobject)
+
+
+### How to insert a `null`?
+
+There are two ways to serialize a `null`:
+
+* either set the value to `(char*)0`,
+* or set the value to `RawJson("null")`
+
+For example, to generate the following JSON:
+
+```json
+{"myValue":null}
+```
+
+you can write:
+
+```c++
+DynamicJsonBuffer jsonBuffer;
+JsonObject& root = jsonBuffer.createObject();
+root["myValue"] = (char*)0; // or (char*)NULL if you prefer
+root.printTo(Serial);
+```
+
+See:
+
+* issue [#418](https://github.com/bblanchon/ArduinoJson/issues/418)
+
 
 
 ### The first serialization succeeds, why do the next ones fail?