Pipeline Poll SCM triggering build without previous parameters

[Surya Prasad]

parameters {

        string(name: 'stageName')

        string(name: 'functionName')

        string(defaultValue: 'sonarqube', name: 'toolName')

        string(name: 'gitCredentialsId')

        string(name: 'gitUrl')

        string(name: 'awsCredentialsId')

        string(defaultValue: 'us-west-2', name: 'awsRegion')

        string(defaultValue: 's3event.sh', name: 's3ShellScript')

        string(defaultValue: 'serverless-nodejs', name: 'nodejsInstallation')

        choice(name: 'Invoke_Parameters', choices:"Yes\nNo", description: "Do you whish to do a dry run to grab parameters?" )

        choice(name: 'SonarQube_Scanning', choices:"Yes\nNo")

    }

    triggers {

        pollSCM('*/2 * * * *')

    }

Parameters and triggers section of the pipeline

The pipeline goes through the stages fine when manually started by giving the parameters. But, on an SCM change, the build is triggered with null values except the parameters with defaultValues.

I assumed that a new build triggered by an SCM change would use the last known good parameters to build. 

Any help will be appreciated.

Thank you.