Problem statement

When using the maxProperties property in a schema, then generated validation logic incorrectly checks the length of the base object as opposed to the length of the property that's being validated.

func (m *SomeThing) validateData(formats strfmt.Registry) error {
	if swag.IsZero(m.Data) { // not required
		return nil
	}

	nprops := len(m) // <-- ERROR: len(m) should be len(m.Data)

	// maxProperties: 20
	if nprops > 20 {
		return errors.TooManyProperties("data", "body", 20)
	}

	return nil
}

Swagger specification

    "SomeThing": {
      "properties": {
        "data": {
          "additionalProperties": {
            "type": "object"
          },
          "maxProperties": 20,
          "type": "object",
          "x-nullable": true
        }
      },
      "type": "object"
    },

Steps to reproduce

1. Create a schema with a component schema that has the above content
2. Generate models swagger generate models -f ./spec.json -t ./out
3. Generated code is non-compilable.

Environment

swagger version: v0.26.1
go version: go1.16.4 darwin/amd64
OS: MacOS