Properly handle empty value for chronic duration attribute

app/models/concerns/chronic_duration_attribute.rb

@@ -10,14 +10,20 @@ module ChronicDurationAttribute
     def chronic_duration_attr_reader(virtual_attribute, source_attribute)
       define_method(virtual_attribute) do
         value = self.send(source_attribute) # rubocop:disable GitlabSecurity/PublicSend
-        ChronicDuration.output(value, format: :short) unless value.nil?
+
+        return '' if value.nil?
+
+        ChronicDuration.output(value, format: :short)
       end
     end
 
     def chronic_duration_attr_writer(virtual_attribute, source_attribute)
       define_method("#{virtual_attribute}=") do |value|
         new_value = ChronicDuration.parse(value).to_i
+        new_value = nil if new_value <= 0
+
         self.send("#{source_attribute}=", new_value) # rubocop:disable GitlabSecurity/PublicSend
+
         new_value
       end
     end

spec/models/concerns/chronic_duration_attribute_spec.rb

@@ -5,11 +5,17 @@ shared_examples 'ChronicDurationAttribute reader' do
     expect(subject.class).to be_public_method_defined(virtual_field)
   end
 
-  it 'outputs chronic duration formated value' do
+  it 'outputs chronic duration formatted value' do
     subject.send("#{source_field}=", 120)
 
     expect(subject.send(virtual_field)).to eq('2m')
   end
+
+  it 'outputs empty string when value set to nil' do
+    subject.send("#{source_field}=", nil)
+
+    expect(subject.send(virtual_field)).to be_empty
+  end
 end
 
 shared_examples 'ChronicDurationAttribute writer' do
@@ -18,10 +24,16 @@ shared_examples 'ChronicDurationAttribute writer' do
   end
 
   it 'parses chronic duration input' do
-    subject.send("#{virtual_field}=", "10m")
+    subject.send("#{virtual_field}=", '10m')
 
     expect(subject.send(source_field)).to eq(600)
   end
+
+  it 'writes null when empty input is used' do
+    subject.send("#{virtual_field}=", '')
+
+    expect(subject.send(source_field)).to be_nil
+  end
 end
 
 describe 'ChronicDurationAttribute' do