this._inscritos.foreach is not a function

Categorias.js:12 Uncaught TypeError: this._inscritos.foreach is not a function
    at Categorias.notificar (Categorias.js:12:1)
    at Categorias.adicionarCategoria (Categorias.js:19:1)
    at ListaDeCategorias._handleEventoInput (ListaDeCategorias.jsx:13:1)
    at HTMLUnknownElement.callCallback (react-dom.development.js:3945:1)
    at Object.invokeGuardedCallbackDev (react-dom.development.js:3994:1)
    at invokeGuardedCallback (react-dom.development.js:4056:1)
    at invokeGuardedCallbackAndCatchFirstError (react-dom.development.js:4070:1)
    at executeDispatch (react-dom.development.js:8243:1)
    at processDispatchQueueItemsInOrder (react-dom.development.js:8275:1)
    at processDispatchQueu

Fala galera beleza?

Pq está ocorrendo este erro? n estou encontrando diferença nos projetos, revi umas 3x rsrs

obrigado