Allow Propshaft assets to use fallbacks

lib/inline_svg/propshaft_asset_finder.rb

@@ -9,7 +9,8 @@ def initialize(filename)
     end
 
     def pathname
-      ::Rails.application.assets.load_path.find(@filename).path
+      asset_path = ::Rails.application.assets.load_path.find(@filename)
+      asset_path.path unless asset_path.nil?
     end
   end
 end

spec/propshaft_asset_finder_spec.rb

@@ -0,0 +1,23 @@
+require_relative '../lib/inline_svg'
+
+describe InlineSvg::PropshaftAssetFinder do
+  context "when the file is not found" do
+    it "returns nil" do
+      stub_const('Rails', double('Rails').as_null_object)
+      expect(::Rails.application.assets.load_path).to receive(:find).with('some-file').and_return(nil)
+
+      expect(InlineSvg::PropshaftAssetFinder.find_asset('some-file').pathname).to be_nil
+    end
+  end
+
+  context "when the file is found" do
+    it "returns fully qualified file paths from Propshaft" do
+      stub_const('Rails', double('Rails').as_null_object)
+      asset = double('Asset')
+      expect(asset).to receive(:path).and_return(Pathname.new('/full/path/to/some-file'))
+      expect(::Rails.application.assets.load_path).to receive(:find).with('some-file').and_return(asset)
+
+      expect(InlineSvg::PropshaftAssetFinder.find_asset('some-file').pathname).to eq Pathname('/full/path/to/some-file')
+    end
+  end
+end