sink(ticdc): fix incorrect encoding default value in Avro protocol (#12018) (#12024)

ref #11994

Author: ti-chi-bot

pkg/sink/codec/avro/avro.go

@@ -558,15 +558,7 @@ func (a *BatchEncoder) columns2AvroSchema(
 				// the string literal "null" must be coerced to a `nil`
 				// see https://github.com/linkedin/goavro/blob/5ec5a5ee7ec82e16e6e2b438d610e1cab2588393/record.go#L109-L114
 				// https://stackoverflow.com/questions/22938124/avro-field-default-values
-				defaultFirst := false
-				if defaultValue == nil {
-					defaultFirst = true
-				} else if s, ok := defaultValue.(string); ok && s == "null" {
-					defaultFirst = true
-				} else if b, ok := defaultValue.([]byte); ok && string(b) == "null" {
-					defaultFirst = true
-				}
-				if defaultFirst {
+				if defaultValue == nil || defaultValue == "null" {
 					field["type"] = []interface{}{"null", avroType}
 				} else {
 					field["type"] = []interface{}{avroType, "null"}

tests/integration_tests/avro_basic/data/data.sql

@@ -168,7 +168,8 @@ create table t1(
     id int primary key,
     c1 varchar(255) default "null",
     c2 varchar(255) default "NULL",
-    c3 varchar(255) default null
+    c3 varchar(255) default null,
+    c4 varbinary(100) DEFAULT b'01101110011101010110110001101100'
 );
 
 insert into t1(id) values(1);