Update google.golang.org/grpc from v1.27.1 to v1.38.0

v1.38.0 is used by Kubernetes since
https://github.com/kubernetes/kubernetes/pull/100488.

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

vendor/google.golang.org/grpc/attributes/attributes.go

@@ -19,7 +19,10 @@
 // Package attributes defines a generic key/value store used in various gRPC
 // components.
 //
-// All APIs in this package are EXPERIMENTAL.
+// Experimental
+//
+// Notice: This package is EXPERIMENTAL and may be changed or removed in a
+// later release.
 package attributes
 
 import "fmt"
@@ -50,6 +53,9 @@ func New(kvs ...interface{}) *Attributes {
 // times, the last value overwrites all previous values for that key.  To
 // remove an existing key, use a nil value.
 func (a *Attributes) WithValues(kvs ...interface{}) *Attributes {
+	if a == nil {
+		return New(kvs...)
+	}
 	if len(kvs)%2 != 0 {
 		panic(fmt.Sprintf("attributes.New called with unexpected input: len(kvs) = %v", len(kvs)))
 	}
@@ -66,5 +72,8 @@ func (a *Attributes) WithValues(kvs ...interface{}) *Attributes {
 // Value returns the value associated with these attributes for key, or nil if
 // no value is associated with key.
 func (a *Attributes) Value(key interface{}) interface{} {
+	if a == nil {
+		return nil
+	}
 	return a.m[key]
 }