Move delete key to coalesceValues and switch to cover all YAML null syntax options

pkg/chartutil/values.go

@@ -278,6 +278,19 @@ func coalesceValues(c *chart.Chart, v map[string]interface{}) (map[string]interf
 	}
 
 	for key, val := range nv {
+		// If the value is YAML null, remove the value's key.
+		// This allows Helm's various sources of values (value files or --set) to
+		// remove incompatible keys from any previous chart, file, or set values.
+		// ref: http://www.yaml.org/spec/1.2/spec.html#id2803362
+		switch val {
+		case "null":
+		case "Null":
+		case "NULL":
+		case "~":
+			delete(v, key)
+			continue
+		}
+
 		if _, ok := v[key]; !ok {
 			// If the key is not in v, copy it from nv.
 			v[key] = val