Test that the coalesced key is properly removed for all YAML null syntax options, but not for empty string

pkg/chartutil/testdata/moby/values.yaml

@@ -2,3 +2,8 @@ scope: moby
 name: moby
 override: bad
 top: nope
+bottom: exists
+right: exists
+left: exists
+front: exists
+back: exists

pkg/chartutil/values_test.go

@@ -277,6 +277,11 @@ func ttpl(tpl string, v map[string]interface{}) (string, error) {
 
 var testCoalesceValuesYaml = `
 top: yup
+bottom: null
+right: Null
+left: NULL
+front: ~
+back: ""
 
 global:
   name: Ishmael
@@ -316,6 +321,7 @@ func TestCoalesceValues(t *testing.T) {
 		expect string
 	}{
 		{"{{.top}}", "yup"},
+		{"{{.back}}", ""},
 		{"{{.name}}", "moby"},
 		{"{{.global.name}}", "Ishmael"},
 		{"{{.global.subject}}", "Queequeg"},
@@ -343,6 +349,13 @@ func TestCoalesceValues(t *testing.T) {
 			t.Errorf("Expected %q to expand to %q, got %q", tt.tpl, tt.expect, o)
 		}
 	}
+
+	nullKeys := []string{"bottom", "right", "left", "front"}
+	for _, nullKey := range nullKeys {
+		if _, ok := v[nullKey]; ok {
+			t.Errorf("Expected key %q to be removed, still present", nullKey)
+		}
+	}
 }
 
 func TestCoalesceTables(t *testing.T) {