r2dbc ReactiveCrudRepository keeps crashing

My pom.xml has the following dependencies:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-r2dbc</artifactId>
  <version>2.3.3.RELEASE</version><!--$NO-MVN-MAN-VER$-->
</dependency>       

<dependency>
            <groupId>io.r2dbc</groupId>
            <artifactId>r2dbc-mssql</artifactId>
            <scope>runtime</scope>
</dependency>

My properties looks like:

spring.r2dbc.url=r2dbc:mssql://localhost:1433/Admin
spring.r2dbc.username=xxx
spring.r2dbc.password=xxx

Repo looks like:

@Repository
public interface UserRepository extends ReactiveCrudRepository<MyUser, String> {
    @Query("SELECT u.Username AS username, u.Password as password FROM Users u INNER JOIN Roles r ON u.RoleId=r.Roleid WHERE u.Username=@username") 
    public Mono<UserDetails> findByUsername(String username);
}

MyUser looks like:

@SuppressWarnings("serial")
public class MyUser implements UserDetails {

    @Id
    private String username;
    private String password;

    public MyUser(String username, String password) {
        this.username = username;
        this.password = password;
    }
    @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {
        return null;
    }

    @Override
    public String getPassword() {
        return password;
    }

    @Override
    public String getUsername() {
        return username;
    }

    @Override
    public boolean isAccountNonExpired() {
        return false;
    }

    @Override
    public boolean isAccountNonLocked() {
        return false;
    }

    @Override
    public boolean isCredentialsNonExpired() {
        return false;
    }

    @Override
    public boolean isEnabled() {
        return true;
    }

I turned on the SQL profiler and caught the query coming in, and it is 100% correct and returns the correct data, but it seems to be crashing on the deserialization. I set a breakpoint and it never calls the MyUser contructor. If I manually create one with Mono.just(), the app works as expected.

I am getting the following exception:

java.lang.NullPointerException: null
    at org.springframework.data.r2dbc.core.DefaultDatabaseClient$DefaultTypedExecuteSpec.lambda$new$0(DefaultDatabaseClient.java:590) ~[spring-data-r2dbc-1.1.3.RELEASE.jar:1.1.3.RELEASE]
    Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
    |_ checkpoint ⇢ org.springframework.security.web.server.authentication.AuthenticationWebFilter [DefaultWebFilterChain]
    |_ checkpoint ⇢ org.springframework.security.web.server.authentication.AuthenticationWebFilter [DefaultWebFilterChain]
    |_ checkpoint ⇢ org.springframework.security.web.server.context.ReactorContextWebFilter [DefaultWebFilterChain]
    |_ checkpoint ⇢ org.springframework.security.web.server.header.HttpHeaderWriterWebFilter [DefaultWebFilterChain]
    |_ checkpoint ⇢ org.springframework.security.config.web.server.ServerHttpSecurity$ServerWebExchangeReactorContextWebFilter [DefaultWebFilterChain]
    |_ checkpoint ⇢ org.springframework.security.web.server.WebFilterChainProxy [DefaultWebFilterChain]
    |_ checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
    |_ checkpoint ⇢ HTTP POST "/login?error" [ExceptionHandlingWebHandler]
Stack trace:
        at org.springframework.data.r2dbc.core.DefaultDatabaseClient$DefaultTypedExecuteSpec.lambda$new$0(DefaultDatabaseClient.java:590) ~[spring-data-r2dbc-1.1.3.RELEASE.jar:1.1.3.RELEASE]
        at java.base/java.util.function.BiFunction.lambda$andThen$0(BiFunction.java:70) ~[na:na]
        at io.r2dbc.mssql.MssqlResult.lambda$map$2(MssqlResult.java:169) ~[r2dbc-mssql-0.8.4.RELEASE.jar:0.8.4.RELEASE]

Any ideas on the what the issue is? The exception is on this block of code:

    if (typeToRead.isInterface()) {
        this.mappingFunction = ColumnMapRowMapper.INSTANCE
                .andThen(map -> projectionFactory.createProjection(typeToRead, map));
    } else {
        this.mappingFunction = dataAccessStrategy.getRowMapper(typeToRead);
    }