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Fixed it by catching the error & ignoring it instead. This workaround only prevented the error, but would introduce another issue... the animation would be renamed & never found if you removed the leading - from it's name. As for why this happens with the theme: https://github.com/NativeScript/theme/blob/15220c0f61fdd7d0bf25aaf9acaa215c69a8c128/src/scss/mixins/components/_button.scss#L221-L243

The $animation is set to "" by default, so ends up generating

animation: -hightlight-light .3s ease-out forwards;

Which is then treated as a number here: https://github.com/hookhookun/parse-animation-shorthand/blob/2a54be6c659115bced4f198d90fe7e3be884711b/src/parseSingleAnimationShorthand.ts#L52-L64

and throwing at the else condition.