ref(pkg/chartutil): replace use of 'fmt.Efforf'

'fmt.Errorf' is unnecessary when checking for 0 length path in Values.PathValue
due to the lack of formatting. Add test covering changes.

pkg/chartutil/values.go

@@ -17,6 +17,7 @@ limitations under the License.
 package chartutil
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -390,7 +391,7 @@ func istable(v interface{}) bool {
 // PathValue takes a yaml path with . notation and returns the value if exists
 func (v Values) PathValue(ypath string) (interface{}, error) {
 	if len(ypath) == 0 {
-		return nil, fmt.Errorf("yaml path string cannot be zero length")
+		return nil, errors.New("yaml path string cannot be zero length")
 	}
 	yps := strings.Split(ypath, ".")
 	if len(yps) == 1 {

pkg/chartutil/values_test.go

@@ -447,10 +447,12 @@ chapter:
 	if _, err := d.PathValue("chapter.doesntexist.one"); err == nil {
 		t.Errorf("Non-existent key in middle of path should return error: %s\n%v", err, d)
 	}
+	if _, err := d.PathValue(""); err == nil {
+		t.Errorf("Empty path should return error: %s\n%v", err, d)
+	}
 	if v, err := d.PathValue("title"); err == nil {
 		if v != "Moby Dick" {
 			t.Errorf("Failed to return values for root key title")
 		}
 	}
-
 }