What means message 'what means task has not declared any outputs'?

There is for instance simple task like

task echoBuildParameters {
doLast {
println project.myprop

During execution seen the output message

‘Task has not declared any outputs’

What does it mean this message?

This message means that the task did not declare its outputs. Gradle uses the inputs and the outputs of a task to determine if the task needs to be executed or not (up-to-date).
For more information have a look at the corresponding userguide section: https://docs.gradle.org/4.0/userguide/more_about_tasks.html#sec:up_to_date_checks.

Thank you for helping, Stefan!