Jenkins pipelines set defaultValue on parameter dynamically

Question

I have jenkinsfile and I want to set defaultValue on the imageTag dynamically, which I'm fetching from the pom file.

Here is the file:

def gr

pipeline {

    agent any

    image = readMavenPom().getParent().getVersion()
    parameters {
        string(name: 'imageTag', defaultValue: image, description: 'Docker image tag')
    }

    stages {
        stage('Environment') {
            steps {
                script {
                    gr = load 'src/ci/script.groovy';
                    echo("Using imageTag: ${params.imageTag}")
                }
            }
        }
     }

I'm getting an error:

startup failed: WorkflowScript: 10: Not a valid section definition: "image = readMavenPom().getParent().getVersion()". Some extra configuration is required. @ line 10, column 5. image = readMavenPom().getParent().getVersion() ^

1 error

at org.codehaus.groovy.control.ErrorCollector.failIfErrors(ErrorCollector.java:310) at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1085) at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:603) at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:581) at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:558) at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:298) at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:268) at groovy.lang.GroovyShell.parseClass(GroovyShell.java:688) at groovy.lang.GroovyShell.parse(GroovyShell.java:700) at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.doParse(CpsGroovyShell.java:142) at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.reparse(CpsGroovyShell.java:127) at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.parseScript(CpsFlowExecution.java:571) at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.start(CpsFlowExecution.java:523) at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:337) at hudson.model.ResourceController.execute(ResourceController.java:97) at hudson.model.Executor.run(Executor.java:429) Finished: FAILURE

I found this solution and it works, but the main idea was setting defaultValue dynamically directly on parameter

    stage('Environment') {
        steps {
            script {
                gr = load 'src/ci/script.groovy';
                version = readMavenPom().getParent().getVersion()

                if (!params.imageTag) {
                    imageTag = version
                }

                echo("Using imageTag: ${imageTag}")
            }
        }
    }