diff --git a/app/models/expert.rb b/app/models/expert.rb
index 01042c840..4574a474f 100644
--- a/app/models/expert.rb
+++ b/app/models/expert.rb
@@ -38,6 +38,8 @@ class Expert < ApplicationRecord
   end
 
   def merge(old_expert)
+    return if old_expert.nil?
+
     procedure_with_new, procedure_without_new = old_expert
       .procedures
       .partition { |p| p.experts.exists?(id) }
diff --git a/app/models/instructeur.rb b/app/models/instructeur.rb
index e9b4c5985..0a3da5b33 100644
--- a/app/models/instructeur.rb
+++ b/app/models/instructeur.rb
@@ -252,6 +252,8 @@ class Instructeur < ApplicationRecord
   end
 
   def merge(old_instructeur)
+    return if old_instructeur.nil?
+
     old_instructeur
       .assign_to
       .where.not(groupe_instructeur_id: assign_to.pluck(:groupe_instructeur_id))
diff --git a/spec/models/expert_spec.rb b/spec/models/expert_spec.rb
index 5b3ebf607..3a27f23aa 100644
--- a/spec/models/expert_spec.rb
+++ b/spec/models/expert_spec.rb
@@ -19,6 +19,12 @@ RSpec.describe Expert, type: :model do
 
     subject { new_expert.merge(old_expert) }
 
+    context 'when the old expert does not exist' do
+      let(:old_expert) { nil }
+
+      it { expect { subject }.not_to raise_error }
+    end
+
     context 'when an old expert access a procedure' do
       let(:procedure) { create(:procedure) }
 
@@ -28,7 +34,7 @@ RSpec.describe Expert, type: :model do
       end
 
       it 'transfers the access to the new expert' do
-        expect(procedure.reload.experts). to match_array(new_expert)
+        expect(procedure.reload.experts).to match_array(new_expert)
       end
     end
 
diff --git a/spec/models/instructeur_spec.rb b/spec/models/instructeur_spec.rb
index a9ffc2c4a..768feef92 100644
--- a/spec/models/instructeur_spec.rb
+++ b/spec/models/instructeur_spec.rb
@@ -743,6 +743,12 @@ describe Instructeur, type: :model do
 
     subject { new_instructeur.merge(old_instructeur) }
 
+    context 'when the old instructeur does not exist' do
+      let(:old_instructeur) { nil }
+
+      it { expect { subject }.not_to raise_error }
+    end
+
     context 'when an procedure is assigned to the old instructeur' do
       let(:procedure) { create(:procedure) }