Fix regression in option validation

Option validation relied on the value being false, not nil, even though
normalizing a string to a Boolean doesn't make sense. Normalizing to an
empty string seems to work fine.

lib/msf/core/opt.rb

@@ -25,7 +25,7 @@ module Msf
       Msf::OptPort.new(__method__.to_s, [ required, desc, default ])
     end
 
-    # @return [OptAddress]
+    # @return [OptAddressLocal]
     def self.LHOST(default=nil, required=true, desc="The listen address")
       Msf::OptAddressLocal.new(__method__.to_s, [ required, desc, default ])
     end
@@ -40,7 +40,7 @@ module Msf
       Msf::OptString.new(__method__.to_s, [ required, desc, default ])
     end
 
-    # @return [OptAddress]
+    # @return [OptAddressRange]
     def self.RHOST(default=nil, required=true, desc="The target address")
       Msf::OptAddressRange.new('RHOSTS', [ required, desc, default ], aliases: [ 'RHOST' ])
     end

lib/msf/core/opt_address_local.rb

@@ -5,7 +5,7 @@ module Msf
 
 ###
 #
-# Network address option.
+# Local network address option.
 #
 ###
 class OptAddressLocal < OptAddress
@@ -17,7 +17,7 @@ class OptAddressLocal < OptAddress
     return unless value.kind_of?(String)
     return value unless interfaces.include?(value)
 
-    ip_address = NetworkInterface.addresses(value).values.flatten.map{|x| x['addr']}.select do |addr|
+    addrs = NetworkInterface.addresses(value).values.flatten.map { |x| x['addr'] }.select do |addr|
       begin
         IPAddr.new(addr).ipv4?
       rescue IPAddr::InvalidAddressError
@@ -25,9 +25,9 @@ class OptAddressLocal < OptAddress
       end
     end
 
-    return if ip_address.blank?
+    return '' if addrs.empty?
 
-    ip_address.first
+    addrs.first
   end
 
   def valid?(value, check_empty: true)