service/dynamodb/dynamodbattribute: Support for configuring the marsh…

…alling behavior of empty collections

service/dynamodb/dynamodbattribute/decode.go

@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/dynamodb"
 )
 
@@ -155,6 +156,7 @@ var byteSliceType = reflect.TypeOf([]byte(nil))
 var byteSliceSlicetype = reflect.TypeOf([][]byte(nil))
 var numberType = reflect.TypeOf(Number(""))
 var timeType = reflect.TypeOf(time.Time{})
+var ptrStringType = reflect.TypeOf(aws.String(""))
 
 func (d *Decoder) decode(av *dynamodb.AttributeValue, v reflect.Value, fieldTag tag) error {
 	var u Unmarshaler
@@ -172,23 +174,23 @@ func (d *Decoder) decode(av *dynamodb.AttributeValue, v reflect.Value, fieldTag
 	}
 
 	switch {
-	case len(av.B) != 0:
+	case len(av.B) != 0 || (av.B != nil && d.EnableEmptyCollections):
 		return d.decodeBinary(av.B, v)
 	case av.BOOL != nil:
 		return d.decodeBool(av.BOOL, v)
-	case len(av.BS) != 0:
+	case len(av.BS) != 0 || (av.BS != nil && d.EnableEmptyCollections):
 		return d.decodeBinarySet(av.BS, v)
-	case len(av.L) != 0:
+	case len(av.L) != 0 || (av.L != nil && d.EnableEmptyCollections):
 		return d.decodeList(av.L, v)
-	case len(av.M) != 0:
+	case len(av.M) != 0 || (av.M != nil && d.EnableEmptyCollections):
 		return d.decodeMap(av.M, v)
 	case av.N != nil:
 		return d.decodeNumber(av.N, v, fieldTag)
-	case len(av.NS) != 0:
+	case len(av.NS) != 0 || (av.NS != nil && d.EnableEmptyCollections):
 		return d.decodeNumberSet(av.NS, v)
-	case av.S != nil:
+	case av.S != nil: // DynamoDB does not allow for empty strings, so we do not consider the length or EnableEmptyCollections flag here
 		return d.decodeString(av.S, v, fieldTag)
-	case len(av.SS) != 0:
+	case len(av.SS) != 0 || (av.SS != nil && d.EnableEmptyCollections):
 		return d.decodeStringSet(av.SS, v)
 	}