Assertion Failed: The {{in-element}} helper cannot be used

[allthesignals]

I can get my project to build. I have ember-in-element-polyfill showing as a transitive dependency. Why am I getting this assertion error if I have the polyfill? What am I missing?

"ember-maybe-in-element": "^2.1.0",
"ember-source": "~3.19.0",
ember-in-element-polyfill@^1.0.0

Build Error (broccoli-persistent-filter:Babel > [Babel: ember-maybe-in-element]) in ember-maybe-in-element/components/maybe-in-element.js

/Users/mattgardner/labs-zola/ember-maybe-in-element/components/maybe-in-element.js: Assertion Failed: The {{in-element}} helper cannot be used. ('ember-maybe-in-element/components/maybe-in-element.hbs' @ L1:C39) Error: /Users/mattgardner/labs-zola/ember-maybe-in-element/components/maybe-in-element.js: Assertion Failed: The {{in-element}} helper cannot be used. ('ember-maybe-in-element/components/maybe-in-element.hbs' @ L1:C39)
    at assert (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:1605:15)
    at BlockStatement (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:11260:54)
    at visitNode (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7740:16)
    at visitArray (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7831:20)
    at visitKey (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7808:7)
    at visitNode (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7762:9)
    at visitKey (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7811:20)
    at visitNode (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7762:9)
    at visitArray (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7831:20)
    at visitKey (/Users/mattgardner/labs-zola/node_modules/ember-source/dist/ember-template-compiler.js:7808:7)