Arithmetic operations not supported in Qute templates

eg. {extensions.size + 1} reports a couple errors,

• [{
  "resource": "/Users/fbricon/Dev/projects/marketplace-stats/marketplace-stats/src/main/resources/templates/index.html",
  "owner": "quarkus",
  "severity": 8,
  "message": "Property/method [size+1] not found on class [java.util.Collection<org.fred.vsc.marketplace.statistics.models.Extension>] nor handled by an extension method",
  "startLineNumber": 1,
  "startColumn": 1,
  "endLineNumber": 1,
  "endColumn": 1
  }]
  [{
  "resource": "/Users/fbricon/Dev/projects/marketplace-stats/marketplace-stats/src/main/resources/templates/index.html",
  "owner": "generated_diagnostic_collection_name#6",
  "code": "InvalidVirtualMethod",
  "severity": 8,
  "message": "The virtual method plus in the type StringTemplateExtensions is not applicable for the base object int type.",
  "source": "qute",
  "startLineNumber": 1,
  "startColumn": 18,
  "endLineNumber": 1,
  "endColumn": 19
  }]

But Quarkus/Qute runs fine with it: