updated per code review

Signed-off-by: Patrick Zheng <[email protected]>

Author: Two-Hearts

verification/truststore/truststore.go

@@ -13,6 +13,7 @@ import (
 
 	corex509 "github.com/notaryproject/notation-core-go/x509"
 	"github.com/notaryproject/notation-go/dir"
+	"github.com/notaryproject/notation-go/internal/slice"
 )
 
 // Type is an enum for trust store types supported such as
@@ -64,6 +65,7 @@ func (trustStore *x509TrustStore) GetCertificates(ctx context.Context, storeType
 		if os.IsNotExist(err) {
 			return nil, fmt.Errorf("%q does not exist", path)
 		}
+		return nil, err
 	}
 
 	// throw error if path is not a directory or is a symlink
@@ -130,12 +132,7 @@ func validateCerts(certs []*x509.Certificate, path string) error {
 
 // isValidStoreType checks if storeType is supported
 func isValidStoreType(storeType Type) bool {
-	for _, t := range Types {
-		if storeType == t {
-			return true
-		}
-	}
-	return false
+	return slice.Contains(Types, storeType)
 }
 
 // isValidFileName checks if a file name is cross-platform compatible