undefined/type.go: Formalized requirement for undefined-types being Stringers

v2/common/type.go

@@ -350,7 +350,7 @@ func TranslateStringToType(tagType TagTypePrimitive, valueString string) (value
     }()
 
     if tagType == TypeUndefined {
-        // TODO(dustin): Circle back to this.
+        // The caller should just call String() on the decoded type.
         log.Panicf("undefined-type values are not supported")
     }
 

v2/undefined/type.go

@@ -1,14 +1,8 @@
 package exifundefined
 
 import (
-	"fmt"
-	"strings"
-
-	"crypto/sha1"
 	"encoding/binary"
 
-	"github.com/dsoprea/go-logging"
-
 	"github.com/dsoprea/go-exif/v2/common"
 )
 
@@ -24,6 +18,7 @@ type UndefinedValueEncoder interface {
 
 type EncodeableValue interface {
 	EncoderName() string
+	String() string
 }
 
 // UndefinedValueEncoder knows how to decode an undefined-type tag's value from