Fix JDBC type validation to check for empty strings in Read and Write Postgres schema transform providers (apache#36103)

Author: liferoad

sdks/java/io/jdbc/src/main/java/org/apache/beam/sdk/io/jdbc/providers/ReadFromPostgresSchemaTransformProvider.java

@@ -58,7 +58,7 @@ protected String jdbcType() {
   public @UnknownKeyFor @NonNull @Initialized SchemaTransform from(
       JdbcReadSchemaTransformConfiguration configuration) {
     String jdbcType = configuration.getJdbcType();
-    if (jdbcType != null && !jdbcType.equals(jdbcType())) {
+    if (jdbcType != null && !jdbcType.isEmpty() && !jdbcType.equals(jdbcType())) {
       throw new IllegalArgumentException(
           String.format("Wrong JDBC type. Expected '%s' but got '%s'", jdbcType(), jdbcType));
     }

sdks/java/io/jdbc/src/main/java/org/apache/beam/sdk/io/jdbc/providers/WriteToPostgresSchemaTransformProvider.java

@@ -58,7 +58,7 @@ protected String jdbcType() {
   public @UnknownKeyFor @NonNull @Initialized SchemaTransform from(
       JdbcWriteSchemaTransformConfiguration configuration) {
     String jdbcType = configuration.getJdbcType();
-    if (jdbcType != null && !jdbcType.equals(jdbcType())) {
+    if (jdbcType != null && !jdbcType.isEmpty() && !jdbcType.equals(jdbcType())) {
       throw new IllegalArgumentException(
           String.format("Wrong JDBC type. Expected '%s' but got '%s'", jdbcType(), jdbcType));
     }