Removed nulls

Will have to figure out a good way to handle empty description/descriptionReason. But for now, just avoiding null is good enough.

Author: cgbystrom

src/main/scala/se/uprise/graphql/types/GraphQLMetadata.scala

@@ -2,6 +2,6 @@ package se.uprise.graphql.types
 
 trait GraphQLMetadata {
  def name: String
- def description: String = null
- def deprecationReason: String = null
+ def description: String = ""
+ def deprecationReason: String = ""
 }