Filtering out null/empty entries in GROQ subqueries for array fields in Sanity.io

export default {
	name: 'page',
	title: 'Page',
	type: 'document',
	fields: [
		{
			name: 'content',
			type:'array', 
			of: 
			[
				{ type: 'page-block-hero' },
				{ type: 'page-block-text' },
				{ type: 'page-block-image' },
				{ type: 'page-block-video' },
				{ type: 'page-block-cta' },
				{ type: 'page-block-carousel' }
			]
		}
	]
}

*[_type == "page" && slug.current == $slug]
{
		'content': content[]
		{
			'hero': hero->
			{
				heading,
				subheading
			},

			'image': image->
			{
				'src': file.asset->url,
				caption
			}
			...
		}
}

*[_type == "page" && slug.current == $slug]
{
		'content': content[]
		{
			'hero': *[hero.heading != null]
			{
				heading,
				subheading
			},

			'image': *[image.file != null]->
			{
				'src': file.asset->url,
				caption
			}
			...
		}
}