diff --git a/lib/plotrb/base.rb b/lib/plotrb/base.rb
index cc6e90d..be9a77f 100644
--- a/lib/plotrb/base.rb
+++ b/lib/plotrb/base.rb
@@ -141,6 +141,7 @@ def define_multi_val_attributes(*methods)
     end
 
     def classify(name, format=nil)
+      return unless name
       klass = name.to_s.split('_').collect(&:capitalize).join
       if format == :json
         klass[0].downcase + klass[1..-1]
@@ -178,6 +179,7 @@ def collect_attributes
       end
 
       def classify(name, format=nil)
+        return unless name
         klass = name.to_s.split('_').collect(&:capitalize).join
         if format == :json
           klass[0].downcase + klass[1..-1]
diff --git a/lib/plotrb/marks.rb b/lib/plotrb/marks.rb
index 7c39d76..a8aa72d 100644
--- a/lib/plotrb/marks.rb
+++ b/lib/plotrb/marks.rb
@@ -446,7 +446,7 @@ def get_full_field_ref(field)
           elsif extra_fields.include?(field.to_s.split('.')[0].to_sym)
             classify(field, :json)
           else
-            "data.#{field}"
+            "data.#{classify(field, :json)}"
           end
         end
 
diff --git a/lib/plotrb/scales.rb b/lib/plotrb/scales.rb
index 5ef79a9..d3955d0 100644
--- a/lib/plotrb/scales.rb
+++ b/lib/plotrb/scales.rb
@@ -258,6 +258,7 @@ def process_domain_max
 
     def get_data_ref_from_string(ref)
       source, field = ref.split('.', 2)
+      field = classify(field, :json)
       data = ::Plotrb::Kernel.find_data(source)
       if field.nil?
         if data && data.values.is_a?(Array)
@@ -278,9 +279,9 @@ def get_data_ref_from_string(ref)
 
     def get_data_ref_from_data(data)
       if data.values.is_a?(Array)
-        ::Plotrb::Scale::DataRef.new.data(data.name).field('data')
+        ::Plotrb::Scale::DataRef.new.data(classify(data.name)).field('data')
       else
-        ::Plotrb::Scale::DataRef.new.data(data.name).field('index')
+        ::Plotrb::Scale::DataRef.new.data(classify(data.name)).field('index')
       end
     end
 
diff --git a/spec/plotrb/base_spec.rb b/spec/plotrb/base_spec.rb
index acaf63b..6ec9e61 100644
--- a/spec/plotrb/base_spec.rb
+++ b/spec/plotrb/base_spec.rb
@@ -282,6 +282,11 @@ class BazClass
       foo.classify('foo_bar_baz', :json).should == 'fooBarBaz'
     end
 
+    it 'classifies zero-length and nil string correctly' do
+      foo.classify('').should == ''
+      foo.classify(nil).should == nil
+    end
+
   end
 
   describe 'Hash' do
diff --git a/spec/plotrb/scales_spec.rb b/spec/plotrb/scales_spec.rb
index e28a424..d1e8695 100644
--- a/spec/plotrb/scales_spec.rb
+++ b/spec/plotrb/scales_spec.rb
@@ -40,7 +40,7 @@
         ::Plotrb::Data.any_instance.stub(:extra_fields).and_return([])
         subject.send(:process_domain)
         subject.domain.data.should == 'some_data'
-        subject.domain.field.should == 'data.some_field'
+        subject.domain.field.should == 'data.someField'
       end
 
       it 'defaults field to index if not provided' do