Making SessionID nillable when creating a new Link.

Fixes #134

client.go

@@ -1506,19 +1506,19 @@ func LinkReceiverSettle(mode ReceiverSettleMode) LinkOption {
 
 // LinkSessionFilter sets a session filter (com.microsoft:session-filter) on the link source.
 // This is used in Azure Service Bus to filter messages by session ID on a receiving link.
-func LinkSessionFilter(sessionID string) LinkOption {
+func LinkSessionFilter(sessionID *string) LinkOption {
 	// <descriptor name="com.microsoft:session-filter" code="00000013:7000000C"/>
 	return linkSourceFilter("com.microsoft:session-filter", uint64(0x00000137000000C), sessionID)
 }
 
 // LinkSelectorFilter sets a selector filter (apache.org:selector-filter:string) on the link source.
 func LinkSelectorFilter(filter string) LinkOption {
 	// <descriptor name="apache.org:selector-filter:string" code="0x0000468C:0x00000004"/>
-	return linkSourceFilter("apache.org:selector-filter:string", uint64(0x0000468C00000004), filter)
+	return linkSourceFilter("apache.org:selector-filter:string", uint64(0x0000468C00000004), &filter)
 }
 
 // linkSourceFilter sets a filter on the link source.
-func linkSourceFilter(name string, code uint64, value string) LinkOption {
+func linkSourceFilter(name string, code uint64, value *string) LinkOption {
 	nameSym := symbol(name)
 	return func(l *link) error {
 		if l.source == nil {
@@ -1527,10 +1527,18 @@ func linkSourceFilter(name string, code uint64, value string) LinkOption {
 		if l.source.Filter == nil {
 			l.source.Filter = make(map[symbol]*describedType)
 		}
-		l.source.Filter[nameSym] = &describedType{
+
+		describedValue := &describedType{
 			descriptor: code,
-			value:      value,
 		}
+
+		if value == nil {
+			describedValue.value = nil
+		} else {
+			describedValue.value = *value
+		}
+
+		l.source.Filter[nameSym] = describedValue
 		return nil
 	}
 }

client_test.go

@@ -6,6 +6,8 @@ import (
 )
 
 func TestLinkOptions(t *testing.T) {
+	sessionID := "123"
+
 	tests := []struct {
 		label string
 		opts  []LinkOption
@@ -24,7 +26,7 @@ func TestLinkOptions(t *testing.T) {
 				LinkProperty("x-opt-test2", "test2"),
 				LinkProperty("x-opt-test1", "test3"),
 				LinkPropertyInt64("x-opt-test4", 1),
-				LinkSessionFilter("123"),
+				LinkSessionFilter(&sessionID),
 			},
 
 			wantSource: &source{
@@ -35,7 +37,7 @@ func TestLinkOptions(t *testing.T) {
 					},
 					"com.microsoft:session-filter" : {
 						descriptor: binary.BigEndian.Uint64([]byte{0x00, 0x00, 0x00, 0x13, 0x70, 0x00, 0x00, 0x0C}),
-						value:      "123",
+						value:      sessionID,
 					},
 				},
 			},
@@ -45,6 +47,21 @@ func TestLinkOptions(t *testing.T) {
 				"x-opt-test4": int64(1),
 			},
 		},
+		{
+			label: "more-link-filters",
+			opts: []LinkOption{
+				LinkSessionFilter(nil),
+			},
+
+			wantSource: &source{
+				Filter: map[symbol]*describedType{
+					"com.microsoft:session-filter" : {
+						descriptor: binary.BigEndian.Uint64([]byte{0x00, 0x00, 0x00, 0x13, 0x70, 0x00, 0x00, 0x0C}),
+						value: nil,
+					},
+				},
+			},
+		},
 	}
 
 	for _, tt := range tests {