filter_chain: don't try to filter nil files

Fixes #117 (undefined method `sub!' for nil:NilClass)

The problem can be reproduced when airbrake-ruby tries to send an
exception with a backtrace, which couldn't be parsed. In that case we
put the whole frame into `function`, leaving `line` and `file` nil.

CHANGELOG.md

@@ -8,6 +8,8 @@ Airbrake Ruby Changelog
 * Started validating the 'environment' config option (a warning will be printed,
   if it is misconfigured)
   ([#115](https://github.com/airbrake/airbrake-ruby/pull/115))
+* Fixed error while filtering unparseable backtraces
+  ([#120](https://github.com/airbrake/airbrake-ruby/pull/120))
 
 ### [v1.4.6][v1.4.6] (August 18, 2016)
 

lib/airbrake-ruby/filter_chain.rb

@@ -13,7 +13,10 @@ class FilterChain
       notice[:errors].each do |error|
         Gem.path.each do |gem_path|
           error[:backtrace].each do |frame|
-            frame[:file].sub!(/\A#{gem_path}/, '[GEM_ROOT]'.freeze)
+            # If the frame is unparseable, then 'file' is nil, thus nothing to
+            # filter (all frame's data is in 'function' instead).
+            next unless (file = frame[:file])
+            file.sub!(/\A#{gem_path}/, '[GEM_ROOT]'.freeze)
           end
         end
       end
@@ -67,7 +70,8 @@ def root_directory_filter(root_directory)
       proc do |notice|
         notice[:errors].each do |error|
           error[:backtrace].each do |frame|
-            frame[:file].sub!(/\A#{root_directory}/, '[PROJECT_ROOT]'.freeze)
+            next unless (file = frame[:file])
+            file.sub!(/\A#{root_directory}/, '[PROJECT_ROOT]'.freeze)
           end
         end
       end

spec/filter_chain_spec.rb

@@ -152,6 +152,42 @@
             to(change { notice.ignored? }.from(false).to(true))
         end
       end
+
+      context "gem root filter" do
+        let(:ex) do
+          AirbrakeTestError.new.tap do |error|
+            error.set_backtrace(['(unparseable/frame.rb:23)'])
+          end
+        end
+
+        it "does not filter file if it is nil" do
+          config.logger = Logger.new('/dev/null')
+          notice = Airbrake::Notice.new(config, ex)
+
+          expect(notice[:errors].first[:file]).to be_nil
+          expect { @chain.refine(notice) }.
+            not_to change { notice[:errors].first[:file] }
+        end
+      end
+
+      context "root directory filter" do
+        let(:ex) do
+          AirbrakeTestError.new.tap do |error|
+            error.set_backtrace(['(unparseable/frame.rb:23)'])
+          end
+        end
+
+        it "does not filter file if it is nil" do
+          config.logger = Logger.new('/dev/null')
+          config.root_directory = '/bingo/bango'
+          notice = Airbrake::Notice.new(config, ex)
+          filter_chain = described_class.new(config)
+
+          expect(notice[:errors].first[:file]).to be_nil
+          expect { filter_chain.refine(notice) }.
+            not_to change { notice[:errors].first[:file] }
+        end
+      end
     end
   end
 end