add a fix

context.go

@@ -33,6 +33,10 @@ func NewContext(app *App, set *flag.FlagSet, parentCtx *Context) *Context {
 	if parentCtx != nil {
 		c.Context = parentCtx.Context
 		c.shellComplete = parentCtx.shellComplete
+
+		if parentCtx.flagSet == nil {
+			parentCtx.flagSet = &flag.FlagSet{}
+		}
 	}
 
 	c.Command = &Command{}

context_test.go

@@ -380,8 +380,8 @@ func TestContextAttributeAccessing(t *testing.T) {
 	for _, test := range tdata {
 		t.Run(test.testCase, func(t *testing.T) {
 			// setup
-			set := flag.NewFlagSet("test", 0)
-			set.Bool(test.setBoolInput, false, "doc")
+			set := flag.NewFlagSet("some-flag-set-name", 0)
+			set.Bool(test.setBoolInput, false, "usage documentation")
 			ctx := NewContext(nil, set, test.newContextInput)
 
 			// logic under test
@@ -389,7 +389,7 @@ func TestContextAttributeAccessing(t *testing.T) {
 
 			// assertions
 			if value != false {
-				t.Errorf("expected test.value to be false, but it was not")
+				t.Errorf("expected \"value\" to be false, but it was not")
 			}
 		})
 	}