containerDefaultToNull=true is not backward compatible

[walaniam]

This PR containerDefaultToNull has changed default behaviour.

Generated code is invalid.

  @Valid
  private List<@Valid PaymentRequestLine> lines;

...

  @NotNull @Valid 
  @Schema(name = "lines", requiredMode = Schema.RequiredMode.REQUIRED)
  @JsonProperty("lines")
public List<@Valid PaymentRequestLine> getLines() {
  return lines;
}

By default there should be empty collection generated (with posibility to override it).