Remove warnings "instance variable @{ivar} not initialized"

lib/omniauth/builder.rb

@@ -3,6 +3,7 @@ require 'omniauth'
 module OmniAuth
   class Builder < ::Rack::Builder
     def initialize(app, &block)
+      @options = nil
       if rack14?
         super
       else

lib/omniauth/form.rb

@@ -95,6 +95,7 @@ module OmniAuth
 
       @html = ""
       @with_custom_button = false
+      @footer = nil
       header(options[:title],options[:header_info])
     end
 

lib/omniauth/strategy.rb

@@ -22,7 +22,7 @@ module OmniAuth
       # Returns an inherited set of default options set at the class-level
       # for each strategy.
       def default_options
-        return @default_options if @default_options
+        return @default_options if instance_variable_defined?(:@default_options) && @default_options
         existing = superclass.respond_to?(:default_options) ? superclass.default_options : {}
         @default_options = OmniAuth::Strategy::Options.new(existing)
       end
@@ -77,9 +77,12 @@ module OmniAuth
       # recorded as. This takes care of 90% of the use cases for overriding
       # the initializer in OmniAuth Strategies.
       def args(args = nil)
-        @args = Array(args) and return if args
+        if args
+          @args = Array(args)
+          return
+        end
         existing = superclass.respond_to?(:args) ? superclass.args : []
-        return @args || existing
+        return (instance_variable_defined?(:@args) && @args) || existing
       end
 
       %w(uid info extra credentials).each do |fetcher|
@@ -123,6 +126,7 @@ module OmniAuth
     # @yield [Options] Yields options to block for further configuration.
     def initialize(app, *args, &block)
       @app = app
+      @env = nil
       @options = self.class.default_options.dup
 
       options.deep_merge!(args.pop) if args.last.is_a?(Hash)