errors are advised to set the function mode to errors.New, consistent with the native go code

[daheige]

trackingmore-sdk-go/errors_enums.go

Line 4 in dd83feb

ErrEmptyAPIKey = "API Key is missing"

[daheige]

adjust code like this:

package trackingmore

import "errors"

var (
	// ErrEmptyAPIKey api key is empty
	ErrEmptyAPIKey                = errors.New("API Key is missing")
	
	// ErrMissingTrackingNumber miss tracking number
	ErrMissingTrackingNumber      = errors.New("Tracking number cannot be empty")
	
	// ErrMissingCourierCode miss courier code
	ErrMissingCourierCode         = errors.New("Courier Code cannot be empty")
	
	// ErrMissingAwbNumber awb number empty
	ErrMissingAwbNumber           = errors.New("Awb number cannot be empty")
	
	// ErrMaxTrackingNumbersExceeded more than 40 tracking numbers
	ErrMaxTrackingNumbersExceeded = errors.New("Max. 40 tracking numbers create in one call")
	
	// ErrEmptyId id empty
	ErrEmptyId                    = errors.New("Id cannot be empty")
	
	// ErrInvalidAirWaybillFormat air waybill number invalid
	ErrInvalidAirWaybillFormat    = errors.New("The air waybill number format is invalid")
)

err can be returned directly where it Is used, so that for third-party access, you can directly determine the type of error by errors.Is func or if err != Errxxx.
daheige@e5d7264