Add default values to APIspec to generate proper models.

APISpecification.yaml

@@ -154,6 +154,7 @@ components:
         feature_type:
           nullable: true
           description: The value of this field is always null. The presence of null in this field will serve as a marker that this is a consequence of an intergenic variant.
+          default: null
         consequences:
           type: array
           items:
@@ -184,6 +185,7 @@ components:
         gene_symbol:
           type: string
           nullable: true
+          default: null
         biotype:
           type: string
         is_canonical:
@@ -218,6 +220,7 @@ components:
         description:
           type: string
           nullable: true
+          default: null
         type:
           type: string
           enum: