return nil if array index indicie is out of bounds

ruby arrays don't throw an exception; they return nil.  Lets do the
same!

this fix also includes the ability to use negative array indicies

1 files changed, 3 insertions, 0 deletions

diff --git a/ruby/Rakefile b/ruby/Rakefile
index 7c1d8495..c25103d8 100644
--- a/ruby/Rakefile
+++ b/ruby/Rakefile
@@ -6,6 +6,9 @@ require "rake/testtask"
 spec = Gem::Specification.load("google-protobuf.gemspec")
 
 if RUBY_PLATFORM == "java"
+  if `which mvn` == ''
+    raise ArgumentError, "maven needs to be installed"
+  end
   task :clean do
     system("mvn clean")
   end