Copy Meterpreter return hash

Dont add a key if no value is found

Author: Meatballs1

lib/msf/core/post/common.rb

@@ -176,7 +176,8 @@ def get_envs(*envs)
     when /shell/
       result = {}
       envs.each do |env|
-        result[env] = get_env(env)
+        res = get_env(env)
+        result[env] = res unless res.blank?
       end
 
       return result