@Entity
public class Argument extends Model
{
    @Id
    public Long id;

    @Required @NotEmpty @Size(max = 140)
    public String summary;

    @SuppressWarnings("unchecked")
    public static Finder<Long, Argument> find = new Finder(Long.class, Argument.class);
    ...
}

@Entity
public class Relation extends Model
{
    @Id
    public Long id;

    @Required @ManyToOne @NotNull @JsonManagedReference
    public Argument from;
    @ManyToOne @JsonManagedReference
    public Argument toArgument;
    @ManyToOne @JsonManagedReference
    public Relation toRelation;
    @Required @NotNull
    public Integer type;
    ...
}

[RuntimeException: java.lang.IllegalArgumentException: Infinite recursion
(StackOverflowError) (through reference chain: models.Argument["relations"]->
com.avaje.ebean.common.BeanList[0]->models.Relation["from"]->
models.Argument["relations"]-> ... ->models.Argument["relations"])
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:611) ~[jackson-databind.jar:2.2.2]
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:142) ~[jackson-databind.jar:2.2.2]
    ...

find.where().or(Expr.eq("from", argument), Expr.eq("toArgument", argument)).findList();

@OneToMany(fetch = FetchType.LAZY, mappedBy = "from") @JsonBackReference
public List<Relation> fromThis;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "toArgument") @JsonBackReference
public List<Relation> toThis;