Ayuda con el error Uncaught TypeError: Cannot read property 'length' of undefined

hello, I am developing a project in vue with c #, the detail is that when sending the data I get the error Uncaught TypeError: Cannot read property ‘length’ of undefined,
someone will help me solve it

so they are in the save method:
.post(“api/Usuarios/Crear”, {
‘idUsuario’: me.idUsuario,
‘nombre’: me.nomUsuario,
‘email’: me.emailUsuario,
‘rol’: me.rol,
‘password’: me.contrasena
so I initialized it

roles: [
{ text: “Administrador”, value: “0” },
{ text: “Tecnico”, value: “1” }
],
idUsuario: “” ,
nomUsuario: “”,
emailUsuario: “”,
rol: “”,
password: “”,
valida: 0,
validaMensaje: [],
and this is the error that the browser responds, which does not send anything to the api

so capture the data

Show your full component code and use syntax highlighting Using Syntax Highlighting in this forum

**Texto en negrita** Usuarios Nuevo {{ formTitle }}
        <v-card-text>
          **<v-container grid-list-md>**

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        <v-card-actions>
          <v-spacer></v-spacer>
          <v-btn color="blue darken-1" flat @click.native="close">Cancelar</v-btn>
          <v-btn color="blue darken-1" flat @click.native="guardar">Guardar</v-btn>
        </v-card-actions>
      </v-card>
    </v-dialog>
  </v-toolbar>
  <v-data-table :headers="headers" :items="usuarios" :search="search" class="elevation-1">
    <template slot="items" slot-scope="props">
      <td class="justify-center layout px-0">
        <v-icon small class="mr-2" @click="editItem(props.item)">edit</v-icon>
      </td>
      <td>{{ props.item.idUsuario }}</td>
      <td>{{ props.item.nomUsuario }}</td>
      <td>{{ props.item.rol }}</td>
      <td>{{ props.item.emailUsuario }}</td>
    </template>
    <template slot="no-data">
      <v-btn color="primary" @click="listar">Resetear</v-btn>
    </template>
  </v-data-table>
</v-flex>

Texto en cursiva