Fix error converting String to BigDecimal

app/models/spree/preference.rb

@@ -22,7 +22,8 @@ module Spree
         when :password
           self[:value].to_s
         when :decimal
-          BigDecimal(self[:value].to_s).round(2, BigDecimal::ROUND_HALF_UP)
+          BigDecimal(self[:value].to_s, exception: false)&.round(2, BigDecimal::ROUND_HALF_UP) ||
+            self[:value]
         when :integer
           self[:value].to_i
         when :boolean

app/models/spree/preferences/preferable.rb

@@ -117,7 +117,7 @@ module Spree
           value.to_s
         when :decimal
           value = 0 if value.blank?
-          BigDecimal(value.to_s).round(2, BigDecimal::ROUND_HALF_UP)
+          BigDecimal(value.to_s, exception: false)&.round(2, BigDecimal::ROUND_HALF_UP) || value
         when :integer
           value.to_i
         when :boolean

spec/models/spree/preference_spec.rb

@@ -58,6 +58,15 @@ describe Spree::Preference do
       expect(pref.value_type).to eq value_type.to_s
     end
 
+    it "incovertible :decimal" do
+      value_type = :decimal
+      value = "invalid"
+      key = "decimal_key"
+      pref = round_trip_preference(key, value, value_type)
+      expect(pref.value).to eq value
+      expect(pref.value_type).to eq value_type.to_s
+    end
+
     it ":string" do
       value_type = :string
       value = "This is a string"

spec/models/spree/preferences/preferable_spec.rb

@@ -165,6 +165,13 @@ describe Spree::Preferences::Preferable do
         @a.set_preference(:if_decimal, '')
         expect(@a.preferences[:if_decimal]).to eq 0.0
       end
+
+      context "when the value cannot be converted to BigDecimal" do
+        it "returns the original value" do
+          @a.set_preference(:if_decimal, "invalid")
+          expect(@a.preferences[:if_decimal]).to eq "invalid"
+        end
+      end
     end
 
     context "converts boolean preferences to boolean values" do