Custom plugin installed fails to start logstash

I have developed a custom logstash output plugin for cassandra. Gem gets built successfully and plugin gets installed successfully too. However When I start the logstash, it crashes with the below message:

:message=>"The error reported is: \n Couldn't find any output plugin named 'cassandra'. Are you sure this is correct? Trying to load the cassandra output plugin resulted in this error: no such file to load -- cassandra"}

My plugin gemspec is as below: do |s| = 'logstash-output-cassandra'
  s.version         = "0.0.1"
  s.licenses = ["Apache License (2.0)"]
  s.summary = "This example output lets you store your data to Cassandra"
  s.description = "This gem is a logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/plugin install gemname. This gem is not a stand-alone program"
  s.authors = ["Elastic"] = ""
  s.homepage = ""
  s.require_paths = ["lib"]

  # Files
  s.files = ["lib/logstash/outputs/cassandra.rb"]
   # Tests
  s.test_files = s.files.grep(%r{^(test|spec|features)/})

  # Special flag to let us know this is actually a logstash plugin
  #s.metadata = { "logstash_plugin" => "true", "logstash_group" => "output" }

  # Gem dependencies
  s.add_runtime_dependency "logstash-core", ">= 1.4.2", "<= 2.1.0"
  s.add_runtime_dependency "logstash-codec-plain", ">=0", "<= 3.0.0"
  s.add_runtime_dependency "cassandra-driver", ">=0", "<= 3.0.0"
  s.add_runtime_dependency "ione", "~>1.2"
  s.add_development_dependency "bundler", "~>1.6"
  s.add_development_dependency "rake", "~>10.0"
  s.add_development_dependency "logstash-devutils"

My plugin code is as below:

# encoding: utf-8
require "logstash/outputs/base"
require "logstash/namespace"
require "cassandra"

class LogStash::Outputs::Cassandra < LogStash::Outputs::Base
  config_name "cassandra"

  # The keyspace to write to
  config :keyspace, :validate => :string, :required => true

 # Credentials for Cassandra DB:

  config :username, :validate => :string, :default => "sonus", :required => true
  config :password, :validate => :string, :default => "Sonus@123", :required => true
  # The column family to write to
  config :table, :validate => :string

  # Cluster connection options
  # If no connection options provided, connects to localhost by default
  # (See
  # for the full list of options)
  config :connection_options, :validate => :hash

  # A mapping from event fields to column names
  # config :event_schema, :validate => :hash, :required => true

  # Index tables for efficient searching of the data
  # The index table should include only two fields the event_id (by default)
  # and an additional field and they should form a composite key
  # e.g CREATE TABLE search_by_host (id uuid, host text) PRIMARY KEY (id, host)
  # config :index_tables, :validate => :hash

  def register
    @connection_options ||= {}

    cluster = Cassandra.cluster(@connection_options)
    @session = cluster.connect(@keyspace)

  end # def register
  def receive(event)
  return unless output?(event)

                recordsMapFromEvent = event.to_hash
                event_id = nil;
                if(recordsMapFromEvent.has_key? "uuid")
                        event_id = recordsMapFromEvent["uuid"]
                if(event_id == nil)
                        event_id = (
                if(recordsMapFromEvent.has_key? "type" and recordsMapFromEvent["type"]=="stats")
                        statType = recordsMapFromEvent["statType"]
                        hostName = recordsMapFromEvent["host"]
                        timeStamp = recordsMapFromEvent["TIMESTAMP"]
                        rejectKeys = ['beat','count','input_type','offset','version','source','type','statType','host']
                        mapCopy = recordsMapFromEvent
                        rejectKeys.each { |k| mapCopy.delete k}
                        insert = @session.prepare("INSERT INTO statistics(uid ,host ,statstype ,datetimestamp ,statistics) VALUES(?,?,?,?,?,?,?,?,?,?,?,?,?)")
                        @session.execute(insert, arguments: [event_id, hostName, statType, timeStamp, mapCopy])
                end #end top if
    end # end begin

  end # def receive
end # class LogStash::Outputs::Cassandra

Please suggest how to proceed further. I am struck here for the past couple of days. Please revert if you require any further info.

@vinod8427 Hi vinod. have you fixed this issue?
Can you please update how to fix the issue.
Thanks in advance.