Error when building Unity+MRTK3.0 project: 'The type or namespace name 'EyesPose' could not be found'

I am building a project with Unity+MRTK3.0, and I am getting an error that states: 'The type or namespace name 'EyesPose' could not be found'. However, the script 'EyeCalibrationChecker' has 'using Windows.UI.Input.Spatial'. The error message shows:I am building a project with Unity+MRTK3.0, and I am getting an error that states: 'The type or namespace name 'EyesPose' could not be found'. However, the script 'EyeCalibrationChecker' has 'using Windows.UI.Input.Spatial'. The error message shows:

Library\PackageCache\org.mixedrealitytoolkit.input@fd4c2f6aee55\Utilities\EyeCalibration\EyeCalibrationChecker.cs(123,21): error CS0246: The type or namespace name 'EyesPose' could not be found (are you missing a using directive or an assembly reference?)Library\PackageCache\org.mixedrealitytoolkit.input@fd4c2f6aee55\Utilities\EyeCalibration\EyeCalibrationChecker.cs(123,21): error CS0246: The type or namespace name 'EyesPose' could not be found (are you missing a using directive or an assembly reference?)

Library\PackageCache\org.mixedrealitytoolkit.input@fd4c2f6aee55\Utilities\EyeCalibration\EyeCalibrationChecker.cs(123,49): error CS1061: 'SpatialPointerPose' does not contain a definition for 'Eyes' and no accessible extension method 'Eyes' accepting a first argument of type 'SpatialPointerPose' could be found (are you missing a using directive or an assembly reference?)Library\PackageCache\org.mixedrealitytoolkit.input@fd4c2f6aee55\Utilities\EyeCalibration\EyeCalibrationChecker.cs(123,49): error CS1061: 'SpatialPointerPose' does not contain a definition for 'Eyes' and no accessible extension method 'Eyes' accepting a first argument of type 'SpatialPointerPose' could be found (are you missing a using directive or an assembly reference?)