feat!: Directive has nullable description

Author: NeedleInAJayStack

Sources/GraphQL/Type/Directives.swift

@@ -31,15 +31,15 @@ public enum DirectiveLocation: String, Encodable {
  */
 public struct GraphQLDirective {
     public let name: String
-    public let description: String
+    public let description: String?
     public let locations: [DirectiveLocation]
     public let args: [GraphQLArgumentDefinition]
     public let isRepeatable: Bool
     public let astNode: DirectiveDefinition?
 
     public init(
         name: String,
-        description: String = "",
+        description: String? = nil,
         locations: [DirectiveLocation],
         args: GraphQLArgumentConfigMap = [:],
         isRepeatable: Bool = false,