this.errors.concat is not a function

[CodeMd2z]

FormulaForm.vue:32 [Vue warn]: The computed property "errors" is already defined as a prop.
found in
--->

......
Also:
TypeError: this.errors.concat is not a function
at VueComponent.mergedErrors (formulate.esm.js:4:51143)
at Watcher.get (vue.runtime.esm.js:3431:33)
at Watcher.evaluate (vue.runtime.esm.js:3532:27)
at VueComponent.computedGetter [as mergedErrors] (vue.runtime.esm.js:5497:25)
at VueComponent.visibleErrors (formulate.esm.js:4:51225)
at Watcher.get (vue.runtime.esm.js:3431:33)
at Watcher.evaluate (vue.runtime.esm.js:3532:27)
at VueComponent.computedGetter [as visibleErrors] (vue.runtime.esm.js:5497:25)
at Object.get (vue.runtime.esm.js:5291:26)
at Proxy.it (formulate.esm.js:4:52484)