Handle nil being passed as uri

lib/fastimage.rb

@@ -85,6 +85,8 @@ class SizeNotFound < FastImageException # :nodoc:
   end
   class CannotParseImage < FastImageException # :nodoc:
   end
+  class BadImageURI < FastImageException # :nodoc:
+  end
 
   DefaultTimeout = 2 unless const_defined?(:DefaultTimeout)
 
@@ -228,6 +230,8 @@ def initialize(uri, options={})
       :size
     end
 
+    raise BadImageURI if uri.nil?
+
     @type, @state = nil
 
     if uri.respond_to?(:read)
@@ -254,7 +258,7 @@ def initialize(uri, options={})
     Errno::ENETUNREACH, ImageFetchFailure, Net::HTTPBadResponse, EOFError, Errno::ENOENT,
     OpenSSL::SSL::SSLError
     raise ImageFetchFailure if @options[:raise_on_failure]
-  rescue UnknownImageType
+  rescue UnknownImageType, BadImageURI
     raise if @options[:raise_on_failure]
   rescue CannotParseImage
     if @options[:raise_on_failure]

test/test.rb

@@ -481,4 +481,14 @@ def test_canon_raw_formats_are_not_recognised_as_tiff
       FastImage.size(TestUrl + "a.CRW", :raise_on_failure=>true)
     end
   end
+
+  def test_returns_nil_when_uri_is_nil
+    assert_equal nil, FastImage.size(nil)
+  end
+
+  def test_raises_when_uri_is_nil_and_raise_on_failure_is_set
+    assert_raises(FastImage::BadImageURI) do
+      FastImage.size(nil, :raise_on_failure => true)
+    end
+  end
 end