APIs with no parameters cause invalid reference

[sradforth]

When there are no parameters for an API call it gives an invalid reference to null in the schema

e.g./api/v1/licenses/list with no parameters produced

		"/api/v1/licenses/list": {
			"post": {
				"tags": ["Licenses"],
				"summary": "Shows all licenses that can be applied for. ",
				"consumes": ["application/json"],
				"produces": ["application/json"],
				"parameters": [{
					"in": "body",
					"name": "body",
					"description": "Shows all licenses that can be applied for. ",
					"schema": { "$ref" : "#/definitions/null"}
				}],

i.e. the post.parameters[0].schema.$ref is pointing at #/definitions/null"
This causes swagger to complain when running