Couchdb_changes gives Invalid FieldReference error

[rhmtsang]

[ERROR] 2020-01-17 10:42:26.091 [[main]<couchdb_changes] javapipeline - A plugin had an unrecoverable error. Will restart this plugin.
  Pipeline_id:main
  Plugin: <LogStash::Inputs::CouchDBChanges port=>5984, db=>"test", id=>"af8c8be0aba724009798ec2e4b5483351c071d0d29e5ed20ed3ae659bec775f5", enable_metric=>true, codec=><LogStash::Codecs::Plain id=>"plain_1154f509-278a-41df-8f7f-2f0818163ad9", enable_metric=>true, charset=>"UTF-8">, host=>"localhost", secure=>false, password=><password>, heartbeat=>1000, keep_id=>false, keep_revision=>false, ignore_attachments=>true, always_reconnect=>true, reconnect_delay=>10>
  Error: Invalid FieldReference: `a[href=#logout]`
  Exception: Java::OrgLogstash::FieldReference::IllegalSyntaxException
  Stack: org.logstash.FieldReference$StrictTokenizer.tokenize(FieldReference.java:283)

• Version: 7.5.1
• Operating System: Ubuntu 18.04
• Config File (if you have sensitive info, please remove it):

input {
  couchdb_changes {
    db => test
    port => 5984
  }
}
output {
  stdout {  }
}

• Sample Data:
  The following document in a couchdb database called "test":

{
  "_id": "42bc7e66787c1282fef951fd98000e05",
  "_rev": "1-b9b0bd4f3deb47a66cd4029b997c5c68",
  "selectors": {
    "a[href=#logout]": {
      "click": [
        "doLogout"
      ]
    }
  }
}

• Steps to Reproduce:
  bin/logstash -f <config_file>

Details: https://discuss.elastic.co/t/214685

[rhmtsang]

PR #13 can provide a workaround for this problem.