fix: Handle NULL values in GetStatistics for empty databases (#37)

When GetStatistics is called on an empty database, SQL SUM() returns NULL
which causes a scan error when converting to int. Wrap SUM expressions with
COALESCE to return 0 instead of NULL.

Add TestGetStatistics to verify both empty and populated database cases.

Fixes issue where `bd stats` and MCP stats tool crash on fresh databases.

Signed-off-by: Joshua Shanks <jjshanks@gmail.com>

internal/storage/sqlite/events.go

@@ -107,9 +107,9 @@ func (s *SQLiteStorage) GetStatistics(ctx context.Context) (*types.Statistics, e
 	err := s.db.QueryRowContext(ctx, `
 		SELECT
 			COUNT(*) as total,
-			SUM(CASE WHEN status = 'open' THEN 1 ELSE 0 END) as open,
-			SUM(CASE WHEN status = 'in_progress' THEN 1 ELSE 0 END) as in_progress,
-			SUM(CASE WHEN status = 'closed' THEN 1 ELSE 0 END) as closed
+			COALESCE(SUM(CASE WHEN status = 'open' THEN 1 ELSE 0 END), 0) as open,
+			COALESCE(SUM(CASE WHEN status = 'in_progress' THEN 1 ELSE 0 END), 0) as in_progress,
+			COALESCE(SUM(CASE WHEN status = 'closed' THEN 1 ELSE 0 END), 0) as closed
 		FROM issues
 	`).Scan(&stats.TotalIssues, &stats.OpenIssues, &stats.InProgressIssues, &stats.ClosedIssues)
 	if err != nil {

internal/storage/sqlite/sqlite_test.go

@@ -346,6 +346,76 @@ func TestSearchIssues(t *testing.T) {
 	}
 }
 
+func TestGetStatistics(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	// Test statistics on empty database (regression test for NULL handling)
+	stats, err := store.GetStatistics(ctx)
+	if err != nil {
+		t.Fatalf("GetStatistics failed on empty database: %v", err)
+	}
+
+	if stats.TotalIssues != 0 {
+		t.Errorf("Expected 0 total issues, got %d", stats.TotalIssues)
+	}
+	if stats.OpenIssues != 0 {
+		t.Errorf("Expected 0 open issues, got %d", stats.OpenIssues)
+	}
+	if stats.InProgressIssues != 0 {
+		t.Errorf("Expected 0 in-progress issues, got %d", stats.InProgressIssues)
+	}
+	if stats.ClosedIssues != 0 {
+		t.Errorf("Expected 0 closed issues, got %d", stats.ClosedIssues)
+	}
+
+	// Create some issues to verify statistics work with data
+	issues := []*types.Issue{
+		{Title: "Open task", Status: types.StatusOpen, Priority: 1, IssueType: types.TypeTask},
+		{Title: "In progress task", Status: types.StatusInProgress, Priority: 1, IssueType: types.TypeTask},
+		{Title: "Closed task", Status: types.StatusClosed, Priority: 1, IssueType: types.TypeTask},
+		{Title: "Another open task", Status: types.StatusOpen, Priority: 2, IssueType: types.TypeTask},
+	}
+
+	for _, issue := range issues {
+		err := store.CreateIssue(ctx, issue, "test-user")
+		if err != nil {
+			t.Fatalf("CreateIssue failed: %v", err)
+		}
+		// Close the one that should be closed
+		if issue.Title == "Closed task" {
+			err = store.CloseIssue(ctx, issue.ID, "Done", "test-user")
+			if err != nil {
+				t.Fatalf("CloseIssue failed: %v", err)
+			}
+		}
+	}
+
+	// Get statistics with data
+	stats, err = store.GetStatistics(ctx)
+	if err != nil {
+		t.Fatalf("GetStatistics failed with data: %v", err)
+	}
+
+	if stats.TotalIssues != 4 {
+		t.Errorf("Expected 4 total issues, got %d", stats.TotalIssues)
+	}
+	if stats.OpenIssues != 2 {
+		t.Errorf("Expected 2 open issues, got %d", stats.OpenIssues)
+	}
+	if stats.InProgressIssues != 1 {
+		t.Errorf("Expected 1 in-progress issue, got %d", stats.InProgressIssues)
+	}
+	if stats.ClosedIssues != 1 {
+		t.Errorf("Expected 1 closed issue, got %d", stats.ClosedIssues)
+	}
+	if stats.ReadyIssues != 2 {
+		t.Errorf("Expected 2 ready issues (open with no blockers), got %d", stats.ReadyIssues)
+	}
+}
+
 // Note: High-concurrency stress tests were removed as the pure Go SQLite driver
 // (modernc.org/sqlite) can experience "database is locked" errors under extreme
 // parallel load (100+ simultaneous operations). This is a known limitation and