Fix a bug with ID generation for series with no tags. (#1392)

src/query/models/tags.go

@@ -49,9 +49,17 @@ func EmptyTags() Tags {
 }
 
 // ID returns a byte slice representation of the tags, using the generation
-// strategy from .
+// strategy from the tag options.
 func (t Tags) ID() []byte {
 	schemeType := t.Opts.IDSchemeType()
+	if len(t.Tags) == 0 {
+		if schemeType == TypeQuoted {
+			return []byte("{}")
+		}
+
+		return []byte("")
+	}
+
 	switch schemeType {
 	case TypeLegacy:
 		return t.legacyID()

src/query/models/tags_test.go

@@ -386,6 +386,24 @@ func buildTags(b *testing.B, count, length int, opts TagOptions, escape bool) Ta
 	return NewTags(count, opts).AddTags(tags)
 }
 
+func TestEmptyTags(t *testing.T) {
+	tests := []struct {
+		idType   IDSchemeType
+		expected string
+	}{
+		{TypeLegacy, ""},
+		{TypePrependMeta, ""},
+		{TypeGraphite, ""},
+		{TypeQuoted, "{}"},
+	}
+
+	for _, tt := range tests {
+		tags := NewTags(0, NewTagOptions().SetIDSchemeType(tt.idType))
+		id := tags.ID()
+		assert.Equal(t, []byte(tt.expected), id)
+	}
+}
+
 var tagBenchmarks = []struct {
 	name                string
 	tagCount, tagLength int