diff --git a/resolver/enum.go b/resolver/enum.go
index ee96fc2b..f6fa160e 100644
--- a/resolver/enum.go
+++ b/resolver/enum.go
@@ -15,10 +15,18 @@ func NewEnumType(enum *Enum, repeated bool) *Type {
 }
 
 func (e *Enum) HasValue(name string) bool {
+	if e == nil {
+		return false
+	}
+
 	return e.Value(name) != nil
 }
 
 func (e *Enum) Value(name string) *EnumValue {
+	if e == nil {
+		return nil
+	}
+
 	if strings.Contains(name, ".") {
 		enumFQDNPrefix := e.FQDN() + "."
 		if !strings.HasPrefix(name, enumFQDNPrefix) {
@@ -48,6 +56,9 @@ func (e *Enum) AttributeMap() map[string][]*EnumValue {
 }
 
 func (e *Enum) Package() *Package {
+	if e == nil {
+		return nil
+	}
 	if e.File == nil {
 		return nil
 	}
@@ -55,6 +66,9 @@ func (e *Enum) Package() *Package {
 }
 
 func (e *Enum) GoPackage() *GoPackage {
+	if e == nil {
+		return nil
+	}
 	if e.File == nil {
 		return nil
 	}
@@ -62,6 +76,9 @@ func (e *Enum) GoPackage() *GoPackage {
 }
 
 func (e *Enum) PackageName() string {
+	if e == nil {
+		return ""
+	}
 	pkg := e.Package()
 	if pkg == nil {
 		return ""
@@ -70,5 +87,9 @@ func (e *Enum) PackageName() string {
 }
 
 func (e *EnumExpr) ReferenceNames() []string {
+	if e == nil {
+		return nil
+	}
+
 	return e.By.ReferenceNames()
 }
diff --git a/resolver/fqdn.go b/resolver/fqdn.go
index 036a6dd4..e14683f1 100644
--- a/resolver/fqdn.go
+++ b/resolver/fqdn.go
@@ -6,14 +6,23 @@ import (
 )
 
 func (s *Service) FQDN() string {
+	if s == nil {
+		return ""
+	}
 	return fmt.Sprintf("%s.%s", s.PackageName(), s.Name)
 }
 
 func (m *Method) FQDN() string {
+	if m == nil {
+		return ""
+	}
 	return fmt.Sprintf("%s/%s", m.Service.FQDN(), m.Name)
 }
 
 func (m *Message) FQDN() string {
+	if m == nil {
+		return ""
+	}
 	return strings.Join(
 		append(append([]string{m.PackageName()}, m.ParentMessageNames()...), m.Name),
 		".",
@@ -21,6 +30,9 @@ func (m *Message) FQDN() string {
 }
 
 func (f *Field) FQDN() string {
+	if f == nil {
+		return ""
+	}
 	if f.Message == nil {
 		return f.Name
 	}
@@ -28,6 +40,9 @@ func (f *Field) FQDN() string {
 }
 
 func (f *OneofField) FQDN() string {
+	if f == nil {
+		return ""
+	}
 	return fmt.Sprintf("%s.%s", f.Oneof.Message.FQDN(), f.Name)
 }
 
@@ -42,10 +57,16 @@ func (e *Enum) FQDN() string {
 }
 
 func (v *EnumValue) FQDN() string {
+	if v == nil {
+		return ""
+	}
 	return fmt.Sprintf("%s.%s", v.Enum.FQDN(), v.Value)
 }
 
 func (t *Type) FQDN() string {
+	if t == nil {
+		return ""
+	}
 	var repeated string
 	if t.Repeated {
 		repeated = "repeated "
@@ -66,5 +87,8 @@ func (t *Type) FQDN() string {
 }
 
 func (n *MessageDependencyGraphNode) FQDN() string {
+	if n == nil {
+		return ""
+	}
 	return fmt.Sprintf("%s_%s", n.BaseMessage.FQDN(), n.VariableDefinition.Name)
 }
diff --git a/resolver/message.go b/resolver/message.go
index ba60c08f..c4da5079 100644
--- a/resolver/message.go
+++ b/resolver/message.go
@@ -74,6 +74,9 @@ func newMessageArgument(msg *Message) *Message {
 }
 
 func (m *Message) ParentMessageNames() []string {
+	if m == nil {
+		return nil
+	}
 	if m.ParentMessage == nil {
 		return []string{}
 	}
@@ -81,6 +84,9 @@ func (m *Message) ParentMessageNames() []string {
 }
 
 func (m *Message) Package() *Package {
+	if m == nil {
+		return nil
+	}
 	if m.File == nil {
 		return nil
 	}
@@ -88,6 +94,9 @@ func (m *Message) Package() *Package {
 }
 
 func (m *Message) HasRule() bool {
+	if m == nil {
+		return false
+	}
 	if m.Rule == nil {
 		return false
 	}
@@ -111,6 +120,9 @@ func (m *Message) IsEnumSelector() bool {
 }
 
 func (m *Message) HasResolvers() bool {
+	if m == nil {
+		return false
+	}
 	if m.Rule == nil {
 		return false
 	}
@@ -135,6 +147,9 @@ func (m *Message) HasResolvers() bool {
 }
 
 func (m *Message) VariableDefinitionGroups() []VariableDefinitionGroup {
+	if m == nil {
+		return nil
+	}
 	if m.Rule == nil {
 		return nil
 	}
@@ -168,6 +183,10 @@ func (m *Message) VariableDefinitionGroups() []VariableDefinitionGroup {
 }
 
 func (m *Message) AllVariableDefinitions() VariableDefinitions {
+	if m == nil {
+		return nil
+	}
+
 	var defs VariableDefinitions
 	for _, group := range m.VariableDefinitionGroups() {
 		defs = append(defs, group.VariableDefinitions()...)
@@ -176,6 +195,9 @@ func (m *Message) AllVariableDefinitions() VariableDefinitions {
 }
 
 func (m *Message) HasCELValue() bool {
+	if m == nil {
+		return false
+	}
 	if m.Rule == nil {
 		return false
 	}
@@ -224,10 +246,18 @@ func (m *Message) HasCELValue() bool {
 }
 
 func (m *Message) HasCustomResolver() bool {
+	if m == nil {
+		return false
+	}
+
 	return m.Rule != nil && m.Rule.CustomResolver
 }
 
 func (m *Message) HasRuleEveryFields() bool {
+	if m == nil {
+		return false
+	}
+
 	for _, field := range m.Fields {
 		if !field.HasRule() {
 			return false
@@ -237,10 +267,18 @@ func (m *Message) HasRuleEveryFields() bool {
 }
 
 func (m *Message) HasCustomResolverFields() bool {
+	if m == nil {
+		return false
+	}
+
 	return len(m.CustomResolverFields()) != 0
 }
 
 func (m *Message) UseAllNameReference() {
+	if m == nil {
+		return
+	}
+
 	if m.Rule == nil {
 		return
 	}
@@ -257,6 +295,10 @@ func (m *Message) UseAllNameReference() {
 }
 
 func (e *MessageExpr) ReferenceNames() []string {
+	if e == nil {
+		return nil
+	}
+
 	var refNames []string
 	for _, arg := range e.Args {
 		refNames = append(refNames, arg.Value.ReferenceNames()...)
@@ -265,6 +307,10 @@ func (e *MessageExpr) ReferenceNames() []string {
 }
 
 func (m *Message) ReferenceNames() []string {
+	if m == nil {
+		return nil
+	}
+
 	if m.Rule == nil {
 		return nil
 	}
@@ -284,6 +330,10 @@ func (m *Message) ReferenceNames() []string {
 }
 
 func (m *Message) CustomResolverFields() []*Field {
+	if m == nil {
+		return nil
+	}
+
 	fields := make([]*Field, 0, len(m.Fields))
 	for _, field := range m.Fields {
 		if field.HasCustomResolver() {
@@ -294,6 +344,9 @@ func (m *Message) CustomResolverFields() []*Field {
 }
 
 func (m *Message) GoPackage() *GoPackage {
+	if m == nil {
+		return nil
+	}
 	if m.File == nil {
 		return nil
 	}
@@ -301,6 +354,9 @@ func (m *Message) GoPackage() *GoPackage {
 }
 
 func (m *Message) PackageName() string {
+	if m == nil {
+		return ""
+	}
 	pkg := m.Package()
 	if pkg == nil {
 		return ""
@@ -309,6 +365,9 @@ func (m *Message) PackageName() string {
 }
 
 func (m *Message) FileName() string {
+	if m == nil {
+		return ""
+	}
 	if m.File == nil {
 		return ""
 	}
@@ -316,10 +375,18 @@ func (m *Message) FileName() string {
 }
 
 func (m *Message) HasField(name string) bool {
+	if m == nil {
+		return false
+	}
+
 	return m.Field(name) != nil
 }
 
 func (m *Message) Field(name string) *Field {
+	if m == nil {
+		return nil
+	}
+
 	for _, field := range m.Fields {
 		if field.Name == name {
 			return field
@@ -329,6 +396,10 @@ func (m *Message) Field(name string) *Field {
 }
 
 func (m *Message) Oneof(name string) *Oneof {
+	if m == nil {
+		return nil
+	}
+
 	for _, field := range m.Fields {
 		if field.Oneof == nil {
 			continue
@@ -341,6 +412,10 @@ func (m *Message) Oneof(name string) *Oneof {
 }
 
 func (m *Message) AllMessages() []*Message {
+	if m == nil {
+		return nil
+	}
+
 	ret := []*Message{m}
 	for _, msg := range m.NestedMessages {
 		ret = append(ret, msg.AllMessages()...)
@@ -349,6 +424,10 @@ func (m *Message) AllMessages() []*Message {
 }
 
 func (m *Message) AllEnums() []*Enum {
+	if m == nil {
+		return nil
+	}
+
 	enums := m.Enums
 	for _, msg := range m.NestedMessages {
 		enums = append(enums, msg.AllEnums()...)
@@ -357,6 +436,10 @@ func (m *Message) AllEnums() []*Enum {
 }
 
 func (m *Message) HasFieldRule() bool {
+	if m == nil {
+		return false
+	}
+
 	for _, field := range m.Fields {
 		if field.HasRule() {
 			return true
@@ -366,6 +449,9 @@ func (m *Message) HasFieldRule() bool {
 }
 
 func (m *Message) DependencyGraphTreeFormat() string {
+	if m == nil {
+		return ""
+	}
 	if m.Rule == nil {
 		return ""
 	}
@@ -373,6 +459,10 @@ func (m *Message) DependencyGraphTreeFormat() string {
 }
 
 func (m *Message) TypeConversionDecls() []*TypeConversionDecl {
+	if m == nil {
+		return nil
+	}
+
 	convertedFQDNMap := make(map[string]struct{})
 	var decls []*TypeConversionDecl
 	for _, def := range m.AllVariableDefinitions() {
@@ -438,6 +528,10 @@ func (m *Message) TypeConversionDecls() []*TypeConversionDecl {
 }
 
 func (m *Message) CustomResolvers() []*CustomResolver {
+	if m == nil {
+		return nil
+	}
+
 	var ret []*CustomResolver
 	if m.HasCustomResolver() {
 		ret = append(ret, &CustomResolver{Message: m})
@@ -459,6 +553,10 @@ func (m *Message) CustomResolvers() []*CustomResolver {
 }
 
 func (m *Message) customResolvers(def *VariableDefinition) []*CustomResolver {
+	if m == nil {
+		return nil
+	}
+
 	var ret []*CustomResolver
 	if def != nil {
 		for _, expr := range def.MessageExprs() {
@@ -472,6 +570,10 @@ func (m *Message) customResolvers(def *VariableDefinition) []*CustomResolver {
 }
 
 func (m *Message) GoPackageDependencies() []*GoPackage {
+	if m == nil {
+		return nil
+	}
+
 	pkgMap := map[*GoPackage]struct{}{}
 	gopkg := m.GoPackage()
 	pkgMap[gopkg] = struct{}{}
@@ -524,6 +626,10 @@ func (m *Message) DependServices() []*Service {
 }
 
 func (m *Message) dependServices(defMap map[*VariableDefinition]struct{}) []*Service {
+	if m == nil {
+		return nil
+	}
+
 	var svcs []*Service
 	for _, def := range m.AllVariableDefinitions() {
 		svcs = append(svcs, dependServicesByDefinition(def, defMap)...)
diff --git a/resolver/resolver.go b/resolver/resolver.go
index 0195d41b..41a05e76 100644
--- a/resolver/resolver.go
+++ b/resolver/resolver.go
@@ -603,12 +603,13 @@ func (r *Resolver) lookupPackageNameMapFromVariableDefinitionSet(defSet *Variabl
 			}
 		case v.Expr.Map != nil:
 			if v.Expr.Map.Expr != nil {
-				if v.Expr.Map.Expr.By != nil {
-					maps.Copy(pkgNameMap, r.lookupPackageNameMapFromCELValue(v.Expr.Map.Expr.By))
+				expr := v.Expr.Map.Expr
+				if expr.By != nil {
+					maps.Copy(pkgNameMap, r.lookupPackageNameMapFromCELValue(expr.By))
 				}
-				if v.Expr.Map.Expr.Message != nil {
-					pkgNameMap[v.Expr.Map.Expr.Message.Message.PackageName()] = struct{}{}
-					maps.Copy(pkgNameMap, r.lookupPackageNameMapFromMessageArguments(v.Expr.Map.Expr.Message.Args))
+				if expr.Message != nil && expr.Message.Message != nil {
+					pkgNameMap[expr.Message.Message.PackageName()] = struct{}{}
+					maps.Copy(pkgNameMap, r.lookupPackageNameMapFromMessageArguments(expr.Message.Args))
 				}
 			}
 		case v.Expr.Validation != nil:
diff --git a/resolver/service.go b/resolver/service.go
index 3c478427..18d98909 100644
--- a/resolver/service.go
+++ b/resolver/service.go
@@ -6,6 +6,9 @@ import (
 )
 
 func (s *Service) GoPackage() *GoPackage {
+	if s == nil {
+		return nil
+	}
 	if s.File == nil {
 		return nil
 	}
@@ -13,6 +16,9 @@ func (s *Service) GoPackage() *GoPackage {
 }
 
 func (s *Service) Package() *Package {
+	if s == nil {
+		return nil
+	}
 	if s.File == nil {
 		return nil
 	}
@@ -20,6 +26,9 @@ func (s *Service) Package() *Package {
 }
 
 func (s *Service) PackageName() string {
+	if s == nil {
+		return ""
+	}
 	pkg := s.Package()
 	if pkg == nil {
 		return ""
@@ -28,6 +37,9 @@ func (s *Service) PackageName() string {
 }
 
 func (s *Service) Method(name string) *Method {
+	if s == nil {
+		return nil
+	}
 	for _, method := range s.Methods {
 		if method.Name == name {
 			return method
@@ -37,6 +49,9 @@ func (s *Service) Method(name string) *Method {
 }
 
 func (s *Service) HasMessageInMethod(msg *Message) bool {
+	if s == nil {
+		return false
+	}
 	for _, mtd := range s.Methods {
 		if mtd.Request == msg {
 			return true
@@ -63,6 +78,9 @@ func (s *Service) HasMessageInVariables(msg *Message) bool {
 }
 
 func (s *Service) GoPackageDependencies() []*GoPackage {
+	if s == nil {
+		return nil
+	}
 	pkgMap := map[*GoPackage]struct{}{}
 	pkgMap[s.GoPackage()] = struct{}{}
 	for _, dep := range s.ServiceDependencies() {
@@ -81,6 +99,9 @@ type CustomResolver struct {
 }
 
 func (r *CustomResolver) FQDN() string {
+	if r == nil {
+		return ""
+	}
 	if r.Field != nil {
 		return fmt.Sprintf("%s.%s", r.Message.FQDN(), r.Field.Name)
 	}
@@ -88,6 +109,9 @@ func (r *CustomResolver) FQDN() string {
 }
 
 func (s *Service) CustomResolvers() []*CustomResolver {
+	if s == nil {
+		return nil
+	}
 	resolverMap := make(map[string]*CustomResolver)
 	for _, method := range s.Methods {
 		for _, resolver := range method.FederationResponse().CustomResolvers() {
@@ -105,10 +129,16 @@ func (s *Service) CustomResolvers() []*CustomResolver {
 }
 
 func (s *Service) ExistsCustomResolver() bool {
+	if s == nil {
+		return false
+	}
 	return len(s.CustomResolvers()) != 0
 }
 
 func (s *Service) ServiceDependencies() []*ServiceDependency {
+	if s == nil {
+		return nil
+	}
 	useServices := s.UseServices()
 	deps := make([]*ServiceDependency, 0, len(useServices))
 	depSvcMap := map[string]*ServiceDependency{}
@@ -124,6 +154,9 @@ func (s *Service) ServiceDependencies() []*ServiceDependency {
 }
 
 func (s *Service) UseServices() []*Service {
+	if s == nil {
+		return nil
+	}
 	svcMap := map[*Service]struct{}{}
 	for _, method := range s.Methods {
 		for _, svc := range method.Response.DependServices() {