Fix errors from new empty regex requirements (#1606)

The merging of #1548 caused issues with two lexers that had been added after the
PR was originally submitted. This commit fixes those errors.

It also reduces the number of calls to `String#upcase` and `String#downcase` in
the Apex lexer (this lexer was updated in #1548).

lib/rouge/lexers/apex.rb

@@ -57,17 +57,19 @@ def self.constants
         rule %r/import\b/, Keyword::Namespace, :import
 
         rule %r/([@$.]?)(#{id})([:(]?)/io do |m|
-          if self.class.keywords.include? m[0].downcase
+          lowercased = m[0].downcase
+          uppercased = m[0].upcase
+          if self.class.keywords.include? lowercased
             token Keyword
-          elsif self.class.soql.include? m[0].upcase
+          elsif self.class.soql.include? uppercased
             token Keyword
-          elsif self.class.declarations.include? m[0].downcase
+          elsif self.class.declarations.include? lowercased
             token Keyword::Declaration
-          elsif self.class.types.include? m[0].downcase
+          elsif self.class.types.include? lowercased
             token Keyword::Type
-          elsif self.class.constants.include? m[0].downcase
+          elsif self.class.constants.include? lowercased
             token Keyword::Constant
-          elsif m[0].downcase == 'package'
+          elsif lowercased == 'package'
             token Keyword::Namespace
           elsif m[1] == "@"
             token Name::Decorator

lib/rouge/lexers/email.rb

@@ -32,7 +32,7 @@ class Email < RegexLexer
       state :root do
         rule %r/\n/, Text
         rule %r/^>.*/, Comment
-        rule %r/.*/, Text
+        rule %r/.+/, Text
       end
     end
   end

lib/rouge/lexers/j.rb

@@ -217,12 +217,12 @@ def self.control_words_id
 
       state :note do
         mixin :delimiter
-        rule %r/.*\n?/, Comment::Multiline
+        rule %r/.+\n?/, Comment::Multiline
       end
 
       state :noun do
         mixin :delimiter
-        rule %r/.*\n?/, Str::Heredoc
+        rule %r/.+\n?/, Str::Heredoc
       end
 
       state :code do