fix: handle empty config values in getRepoConfig() (GH#680)

GetConfig() returns ("", nil) for missing/empty config keys.
getRepoConfig() then tried json.Unmarshal([]byte(""), ...) which
fails with "unexpected end of JSON input".

Add empty value check before JSON parsing - return empty map when
config value is empty string.

Closes GH#680

Co-Authored-By: dylan-conlin <dylan-conlin@users.noreply.github.com>

cmd/bd/repo.go

@@ -196,6 +196,11 @@ func getRepoConfig(ctx context.Context, store storage.Storage) (map[string]strin
 		return nil, err
 	}
 
+	// Handle empty value (config key exists but no value set)
+	if value == "" {
+		return make(map[string]string), nil
+	}
+
 	// Parse JSON map
 	repos := make(map[string]string)
 	if err := json.Unmarshal([]byte(value), &repos); err != nil {

cmd/bd/repo_test.go

@@ -0,0 +1,109 @@
+package main
+
+import (
+	"context"
+	"testing"
+)
+
+func TestGetRepoConfig_EmptyValue(t *testing.T) {
+	ctx := context.Background()
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	// Test 1: No config set at all - should return empty map
+	repos, err := getRepoConfig(ctx, store)
+	if err != nil {
+		t.Fatalf("getRepoConfig with no config failed: %v", err)
+	}
+	if len(repos) != 0 {
+		t.Errorf("Expected empty map, got %d entries", len(repos))
+	}
+
+	// Test 2: Empty string value - should return empty map (this was the bug)
+	// This simulates GetConfig returning ("", nil) which caused "unexpected end of JSON input"
+	err = store.SetConfig(ctx, "repos.additional", "")
+	if err != nil {
+		t.Fatalf("SetConfig failed: %v", err)
+	}
+	repos, err = getRepoConfig(ctx, store)
+	if err != nil {
+		t.Fatalf("getRepoConfig with empty value failed: %v", err)
+	}
+	if len(repos) != 0 {
+		t.Errorf("Expected empty map for empty value, got %d entries", len(repos))
+	}
+
+	// Test 3: Valid JSON value - should parse correctly
+	err = store.SetConfig(ctx, "repos.additional", `{"alias1":"/path/to/repo1","alias2":"/path/to/repo2"}`)
+	if err != nil {
+		t.Fatalf("SetConfig with JSON failed: %v", err)
+	}
+	repos, err = getRepoConfig(ctx, store)
+	if err != nil {
+		t.Fatalf("getRepoConfig with valid JSON failed: %v", err)
+	}
+	if len(repos) != 2 {
+		t.Errorf("Expected 2 repos, got %d", len(repos))
+	}
+	if repos["alias1"] != "/path/to/repo1" {
+		t.Errorf("Expected '/path/to/repo1', got '%s'", repos["alias1"])
+	}
+	if repos["alias2"] != "/path/to/repo2" {
+		t.Errorf("Expected '/path/to/repo2', got '%s'", repos["alias2"])
+	}
+}
+
+func TestSetRepoConfig(t *testing.T) {
+	ctx := context.Background()
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	// Set repos and verify round-trip
+	repos := map[string]string{
+		"planning": "/home/user/planning-repo",
+		"shared":   "/home/user/shared-repo",
+	}
+
+	err := setRepoConfig(ctx, store, repos)
+	if err != nil {
+		t.Fatalf("setRepoConfig failed: %v", err)
+	}
+
+	// Read back
+	result, err := getRepoConfig(ctx, store)
+	if err != nil {
+		t.Fatalf("getRepoConfig after set failed: %v", err)
+	}
+
+	if len(result) != 2 {
+		t.Errorf("Expected 2 repos, got %d", len(result))
+	}
+	if result["planning"] != "/home/user/planning-repo" {
+		t.Errorf("Expected planning repo path, got '%s'", result["planning"])
+	}
+	if result["shared"] != "/home/user/shared-repo" {
+		t.Errorf("Expected shared repo path, got '%s'", result["shared"])
+	}
+}
+
+func TestRepoConfigEmptyMap(t *testing.T) {
+	ctx := context.Background()
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	// Set empty map
+	repos := make(map[string]string)
+	err := setRepoConfig(ctx, store, repos)
+	if err != nil {
+		t.Fatalf("setRepoConfig with empty map failed: %v", err)
+	}
+
+	// Read back - should work and return empty map
+	result, err := getRepoConfig(ctx, store)
+	if err != nil {
+		t.Fatalf("getRepoConfig after empty set failed: %v", err)
+	}
+	if len(result) != 0 {
+		t.Errorf("Expected empty map, got %d entries", len(result))
+	}
+}