{
  "name": "count_missing",
  "type": "function",
  "groups": ["Aggregates"],
  "description": "Returns the count of missing (NULL) values.",
  "arguments": [{
    "arg": "expression",
    "description": "sub expression of field to aggregate"
  }, {
    "arg": "group_by",
    "optional": true,
    "description": "optional expression to use to group aggregate calculations"
  }, {
    "arg": "filter",
    "optional": true,
    "description": "optional expression to use to filter features used to calculate aggregate"
  }],
  "examples": [{
    "expression": "count_missing(\"stations\",group_by:=\"state\")",
    "returns": "count of missing (NULL) station values, grouped by state field"
  }],
  "tags": ["aggregate", "missing", "count"]
}