Context variable 'Event' not available in automation scripting context when triggered on event 'beforeDocumentModification', but it is in automation chain context

When an automation chain is triggered by an event handler on event beforeDocumentModification, a context variable named Event is injected in the automation context, but the context variable Event in an automation scripting is empty.

How to reproduce:

• create an event handler triggered by event before document modification
• when it executes the following automation chain:

  - Context.FetchDocument
  - Log:
      level: warn
      message: "<SUPNXP-18961_printDocumentBeforeModification> Event: @{Event}"
      category: org.nuxeo
  - Log:
      level: warn
      message: "<SUPNXP-18961_printDocumentBeforeModification> document's title before modification: @{Event.context.getProperty(\"previousDocumentModel\").getPropertyValue('dc:title')}"
      category: org.nuxeo
  - Log:
      level: warn
      message: "<SUPNXP-18961_printDocumentBeforeModification> document's title after modification: @{Document['dc:title']}"
      category: org.nuxeo
  

  it generates the following logs:

  14:22:49,738 WARN  [nuxeo] <SUPNXP-18961_printDocumentBeforeModification> Event: org.nuxeo.ecm.core.event.impl.EventImpl@3f993666
  14:22:49,742 WARN  [nuxeo] <SUPNXP-18961_printDocumentBeforeModification> document's title before modification: BLANK.pdf
  14:22:49,742 WARN  [nuxeo] <SUPNXP-18961_printDocumentBeforeModification> document's title after modification: BLANK.pdf2
  14:22:49,794 WARN  [Console] <logDocumentModified> /default-domain/workspaces/ws1/BLANK.pdf
  

• when it executes the following automation scripting:

  function run(input, params) {
    Console.warn('<SUPNXP18961_printDocumentBeforeModification> Event: ' + Event);
    Console.warn('<SUPNXP18961_printDocumentBeforeModification> Event: ' + JSON.stringify(Event)); // EMPTY object, WHY?
    Console.warn('<SUPNXP18961_printDocumentBeforeModification> Event.context: ' + Event.context);
  }
  

  it generates the following logs:

  14:28:06,176 WARN  [Console] <SUPNXP18961_printDocumentBeforeModification> Event: [object Object]
  14:28:06,176 WARN  [Console] <SUPNXP18961_printDocumentBeforeModification> Event: {}
  14:28:06,177 WARN  [Console] <SUPNXP18961_printDocumentBeforeModification> Event.context: undefined
  14:28:06,248 WARN  [Console] <logDocumentModified> /default-domain/workspaces/ws1/BLANK.pdf