Problems converting a JSON string into a 'collection' variable

I am using Camunda Platform 7, I have the following BPMN, where I am trying to convert a JSON string into a “collection” variable using Groovy to use it later in a multi-instance subprocess. However, the variable “miColeccion” is not identified as a “collection” type variable. When deploying it in Camunda, I get the following error: Cannot instantiate process definition Process_1e9o47z:1:4f643a0a-f338-11ed-9f36-64bc58ddeca3: ENGINE-02025 Variable ‘miColeccion’ is not of the expected type ‘Collection’. Could you please guide me?

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This is the string with the JSON: def jsonString = ‘{“expedientes”:[{“idExpediente”:“431626a3-3d99-4eb8-acbe-e6673680e2c8”,“id_expediente_gestor”:33,“id_usuario_actor”:“bfa34eb5-9419-4ba2-a5f7-3e9f61e1da90”,“id_usuario_secretario”:null,“id_usuario_magistrado”:null,“id_usuario_interno”:18,“id_estatus_actor”:“57939f1a-4b0d-433c-bc21-dec4ede0a60c”,“estatus_actor”:“Abierto”,“id_estatus_secretario”:null,“estatus_secretario”:“”,“id_estatus_magistrado”:null,“estatus_magistrado”:“”},{“idExpediente”:“8106c1c0-404d-4311-986c-ee3117fe7702”,“id_expediente_gestor”:34,“id_usuario_actor”:“bfa34eb5-9419-4ba2-a5f7-3e9f61e1da90”,“id_usuario_secretario”:null,“id_usuario_magistrado”:null,“id_usuario_interno”:18,“id_estatus_actor”:“57939f1a-4b0d-433c-bc21-dec4ede0a60c”,“estatus_actor”:“Abierto”,“id_estatus_secretario”:null,“estatus_secretario”:“”,“id_estatus_magistrado”:null,“estatus_magistrado”:“”},{“idExpediente”:“5b9c7a7c-2146-4962-810a-cf9d862c5d16”,“id_expediente_gestor”:35,“id_usuario_actor”:“bfa34eb5-9419-4ba2-a5f7-3e9f61e1da90”,“id_usuario_secretario”:null,“id_usuario_magistrado”:null,“id_usuario_interno”:18,“id_estatus_actor”:“b0420c7e-67aa-4e49-8afa-98530d2eee6b”,“estatus_actor”:“Terminado”,“id_estatus_secretario”:null,“estatus_secretario”:“”,“id_estatus_magistrado”:null,“estatus_magistrado”:“”}]}’

Thank you.