Indicate nullable types for LiveMap IDL

Co-authored-by: Lawrence Forooghian <53756884+lawrence-forooghian@users.noreply.github.com>

Author: VeskeR

textile/objects-features.textile

@@ -274,9 +274,9 @@ class LiveCounter extends LiveObject: // RTLC*, RTLC1
   value() -> Number // RTLC5
 
 class LiveMap extends LiveObject: // RTLM*, RTLM1
-  get(key: String) -> Boolean | Binary | Number | String | JsonArray | JsonObject | LiveCounter | LiveMap // RTLM5
+  get(key: String) -> (Boolean | Binary | Number | String | JsonArray | JsonObject | LiveCounter | LiveMap)? // RTLM5
   size() -> Number // RTLM10
-  entries() -> [String, Boolean | Binary | Number | String | JsonArray | JsonObject | LiveCounter | LiveMap][] // RTLM11
+  entries() -> [String, (Boolean | Binary | Number | String | JsonArray | JsonObject | LiveCounter | LiveMap)?][] // RTLM11
   keys() -> String[] // RTLM12
-  values() -> (Boolean | Binary | Number | String | JsonArray | JsonObject | LiveCounter | LiveMap)[] // RTLM13
+  values() -> (Boolean | Binary | Number | String | JsonArray | JsonObject | LiveCounter | LiveMap)?[] // RTLM13
 </pre>