diff --git a/internal/handler/converter.go b/internal/handler/converter.go
index d3992f9..2208721 100644
--- a/internal/handler/converter.go
+++ b/internal/handler/converter.go
@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"strings"
 	"time"
 
 	api "github.com/fun-dotto/academic-api/generated"
@@ -273,7 +274,9 @@ func timetableSlotToAPI(slot domain.TimetableSlot) api.DottoFoundationV1Timetabl
 
 func timetableItemToAPI(d domain.TimetableItem) api.TimetableItem {
 	var slot *api.DottoFoundationV1TimetableSlot
-	if d.Slot != nil {
+	if d.Slot != nil &&
+		strings.TrimSpace(string(d.Slot.DayOfWeek)) != "" &&
+		strings.TrimSpace(string(d.Slot.Period)) != "" {
 		s := timetableSlotToAPI(*d.Slot)
 		slot = &s
 	}
@@ -304,9 +307,13 @@ func toDomainTimetableItemFromRequest(req api.TimetableItemRequest) domain.Timet
 		Subject: domain.Subject{ID: req.SubjectId},
 	}
 	if req.Slot != nil {
-		item.Slot = &domain.TimetableSlot{
-			DayOfWeek: domain.DayOfWeek(req.Slot.DayOfWeek),
-			Period:    domain.Period(req.Slot.Period),
+		dow := strings.TrimSpace(string(req.Slot.DayOfWeek))
+		per := strings.TrimSpace(string(req.Slot.Period))
+		if dow != "" && per != "" {
+			item.Slot = &domain.TimetableSlot{
+				DayOfWeek: domain.DayOfWeek(dow),
+				Period:    domain.Period(per),
+			}
 		}
 	}
 	rooms := make([]domain.Room, len(req.RoomIds))
diff --git a/internal/handler/converter_timetable_item_test.go b/internal/handler/converter_timetable_item_test.go
new file mode 100644
index 0000000..3e88067
--- /dev/null
+++ b/internal/handler/converter_timetable_item_test.go
@@ -0,0 +1,161 @@
+package handler
+
+import (
+	"testing"
+
+	api "github.com/fun-dotto/academic-api/generated"
+	"github.com/fun-dotto/academic-api/internal/domain"
+)
+
+func TestTimetableItemToAPI_Slot(t *testing.T) {
+	baseSubject := domain.Subject{ID: "subject-1", Name: "Test"}
+
+	tests := []struct {
+		name     string
+		slot     *domain.TimetableSlot
+		wantNil  bool
+		wantDow api.DottoFoundationV1DayOfWeek
+		wantPer api.DottoFoundationV1Period
+	}{
+		{
+			name:    "slot is nil",
+			slot:    nil,
+			wantNil: true,
+		},
+		{
+			name: "both fields empty string",
+			slot: &domain.TimetableSlot{
+				DayOfWeek: "",
+				Period:    "",
+			},
+			wantNil: true,
+		},
+		{
+			name: "dayOfWeek empty",
+			slot: &domain.TimetableSlot{
+				DayOfWeek: "",
+				Period:    domain.PeriodPeriod1,
+			},
+			wantNil: true,
+		},
+		{
+			name: "period empty",
+			slot: &domain.TimetableSlot{
+				DayOfWeek: domain.DayOfWeekMonday,
+				Period:    "",
+			},
+			wantNil: true,
+		},
+		{
+			name: "whitespace only",
+			slot: &domain.TimetableSlot{
+				DayOfWeek: " \t",
+				Period:    "  ",
+			},
+			wantNil: true,
+		},
+		{
+			name: "valid slot",
+			slot: &domain.TimetableSlot{
+				DayOfWeek: domain.DayOfWeekMonday,
+				Period:    domain.PeriodPeriod1,
+			},
+			wantNil: false,
+			wantDow: api.Monday,
+			wantPer: api.Period1,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := timetableItemToAPI(domain.TimetableItem{
+				ID:      "item-1",
+				Subject: baseSubject,
+				Slot:    tt.slot,
+				Rooms:   nil,
+			})
+
+			if tt.wantNil {
+				if got.Slot != nil {
+					t.Fatalf("Slot: got non-nil %+v, want nil", got.Slot)
+				}
+				return
+			}
+			if got.Slot == nil {
+				t.Fatal("Slot: got nil, want non-nil")
+			}
+			if got.Slot.DayOfWeek != tt.wantDow {
+				t.Errorf("DayOfWeek: got %q, want %q", got.Slot.DayOfWeek, tt.wantDow)
+			}
+			if got.Slot.Period != tt.wantPer {
+				t.Errorf("Period: got %q, want %q", got.Slot.Period, tt.wantPer)
+			}
+		})
+	}
+}
+
+func TestToDomainTimetableItemFromRequest_Slot(t *testing.T) {
+	subjectID := "subject-1"
+
+	tests := []struct {
+		name    string
+		slot    *api.DottoFoundationV1TimetableSlot
+		wantNil bool
+	}{
+		{
+			name:    "request slot is nil",
+			slot:    nil,
+			wantNil: true,
+		},
+		{
+			name: "both empty",
+			slot: &api.DottoFoundationV1TimetableSlot{
+				DayOfWeek: "",
+				Period:    "",
+			},
+			wantNil: true,
+		},
+		{
+			name: "whitespace only",
+			slot: &api.DottoFoundationV1TimetableSlot{
+				DayOfWeek: "  ",
+				Period:    "\t",
+			},
+			wantNil: true,
+		},
+		{
+			name: "valid",
+			slot: &api.DottoFoundationV1TimetableSlot{
+				DayOfWeek: api.Tuesday,
+				Period:    api.Period2,
+			},
+			wantNil: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := toDomainTimetableItemFromRequest(api.TimetableItemRequest{
+				SubjectId: subjectID,
+				Slot:      tt.slot,
+				RoomIds:   []string{},
+			})
+
+			if tt.wantNil {
+				if got.Slot != nil {
+					t.Fatalf("Slot: got %+v, want nil", got.Slot)
+				}
+				return
+			}
+			if got.Slot == nil {
+				t.Fatal("Slot: got nil, want non-nil")
+			}
+			if got.Slot.DayOfWeek != domain.DayOfWeekTuesday {
+				t.Errorf("DayOfWeek: got %q", got.Slot.DayOfWeek)
+			}
+			if got.Slot.Period != domain.PeriodPeriod2 {
+				t.Errorf("Period: got %q", got.Slot.Period)
+			}
+		})
+	}
+}