Spring Data Native Query uses VARBINARY for null String @Param

I have a JpaRepository, with a native query in it:

@Query (value = "SELECT t.team_name FROM teams t " +
                "WHERE (:teamcode IS NULL OR t.team_code = :teamcode) ",
                nativeQuery = true)
                List<Object[]> getTeamNames(@Param("teamcode") @Nullable String teamCode);

If I pass a non-null value, it works fine - the binding parameter type is VARCHAR. However, if I pass in a null parameter value, then the binding type is VARBINARY, and the query fails with the error:

SQL Error: 0, SQLState: 42883
ERROR: operator does not exist: character varying = bytea
  Hint: No operator matches the given name and argument types. You might need to add explicit type casts.

Table:

CREATE TABLE teams (
  team_id         BIGINT         NOT NULL,
  team_code       VARCHAR(24)    NOT NULL,
  team_name       VARCHAR(200),
  team_desc       VARCHAR(2000),
)

Entity:

@Entity
@DynamicUpdate
@Getter
@Setter
@EqualsAndHashCode(onlyExplicitlyIncluded = true, callSuper = false)
@Table(name = "teams", schema = "public")
public class Team extends BaseEntity
{
    @Id
    @Column(name = "team_id", nullable = false)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "ent_generator")
    @SequenceGenerator(name = "ent_generator", sequenceName = "entity_seq", allocationSize = 1)
    private long teamId;

    @EqualsAndHashCode.Include
    @Basic
    @Column(name = "team_code", length = 24)
    private String teamCode;

    @Basic
    @Column(name = "team_name", length = 200)
    private String teamName;

    @Basic
    @Column(name = "team_desc", length = 2000)
    private String teamDescription;
}

How do I resolve this?