Simplify code

app/models/champs/carte_champ.rb

@@ -90,6 +90,6 @@ class Champs::CarteChamp < Champ
   end
 
   def for_api
-    geo_json.present? ? geo_json.to_json : nil
+    geo_json&.to_json
   end
 end

app/models/champs/decimal_number_champ.rb

@@ -12,6 +12,6 @@ class Champs::DecimalNumberChamp < Champ
   private
 
   def processed_value
-    value.present? ? value.to_f : nil
+    value&.to_f
   end
 end

app/models/champs/integer_number_champ.rb

@@ -12,6 +12,6 @@ class Champs::IntegerNumberChamp < Champ
   private
 
   def processed_value
-    value.present? ? value.to_i : nil
+    value&.to_i
   end
 end

app/models/champs/multiple_drop_down_list_champ.rb

@@ -10,7 +10,7 @@ class Champs::MultipleDropDownListChamp < Champ
   end
 
   def to_s
-    value.present? ? selected_options.join(', ') : ''
+    selected_options.join(', ')
   end
 
   def for_export