Getting values from an empty yamls should not fail

When getting a value from an empty yaml, GetType tries to get the
kind of nil which makes it fail, this commit covers the nil case
in GetType.

assets/examples/empty.yml

@@ -0,0 +1 @@
+---

pkg/v1/ytbx/common.go

@@ -37,7 +37,8 @@ const (
 // GetType returns the type of the input value with a YAML specific view
 func GetType(value interface{}) string {
 	switch tobj := value.(type) {
-	case yaml.MapSlice:
+
+	case yaml.MapSlice, nil:
 		return typeMap
 
 	case []interface{}:

pkg/v1/ytbx/getting_test.go

@@ -59,4 +59,10 @@ var _ = Describe("getting stuff test cases", func() {
 			Expect(grabError(example, "/yaml/named-entry-list-using-id/id=0")).To(BeEquivalentTo("there is no entry id=0 in the list"))
 		})
 	})
+	Context("Trying to get values by path in an empty file", func() {
+		It("should return a not found key error", func() {
+			emptyFile := yml("../../../assets/examples/empty.yml")
+			Expect(grabError(emptyFile, "does-not-exist")).To(BeEquivalentTo("no key 'does-not-exist' found in map, available keys: "))
+		})
+	})
 })