Twig template variable not displaying value

Question

I have a Twig template for a custom block. My custom module is establishing what template is used like so

function mymodule_theme($existing, $type, $theme, $path){
    return array('mymodule' =>
        array(
            'variables' => array(
                'header-title' => 'Default Title',
                'header-size' => 'h1'
                ), 
                'template' => 'block--HeaderText'
            )
        );
}

and my custom block contains.

public function build() {
    return array(
        '#theme' => 'mymodule',
        '#title' => '',
        '#header-title' => $this->configuration['label'],
        '#header-size' => $this->configuration['header-size-submit'],
        );
}

And in my block--HeaderText.html.twig I have

<h2>{{ header-title }}</h2> This is a test {{ header-size }}
{{ dump() }}

However header-title and header-size both output 0. But using the dump() function in the template shows that the actual variables are available some how.

The dump() produces

array(15) { ["header-title"]=> string(19) "Header Textsdfgsdfg" ["header-size"]=> string(2) "h4"...

Yet {{ header-title }} just results in 0.

Answer 1

The issue was that Drupal didn't like that the variable names had hyphens in them. When switching from header-text to header_text it worked fine.