fix: update GetPage to check for empty items slice

Refactor the GetPage function to check for an empty slice of items 
instead of a nil pointer. Update tests to cover cases for nil and 
empty slices, ensuring consistent behavior and improved clarity.

pagination.go

@@ -52,7 +52,7 @@ func EncodeCursor(cursor string) string {
 }
 
 func GetPage[T any](items []T, first *int, after *string, last *int, before *string, max int, fn func(T) string) ([]T, PageInfo) {
-	if items == nil {
+	if len(items) == 0 {
 		return nil, PageInfo{}
 	}
 	tmp := min(max, len(items))

pagination_test.go

@@ -24,11 +24,17 @@ func TestGetPage(t *testing.T) {
 	}
 	tests := []testCase[string]{
 		{
-			name:         "empty",
+			name:         "nil items",
 			args:         args[string]{max: 10},
 			wantItems:    nil,
 			wantPageInfo: PageInfo{},
 		},
+		{
+			name:         "empty items",
+			args:         args[string]{items: []string{}, max: 10},
+			wantItems:    nil,
+			wantPageInfo: PageInfo{},
+		},
 		{
 			name:      "first 2",
 			args:      args[string]{items: []string{"1", "2", "3"}, first: ptr(2), max: 10, fn: func(s string) string { return s }},