Test that the coalesced key is properly removed for all YAML null syntax...

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) {