Can Java Protocol Buffers ever return null on the list getter of a repeated field?

Question

Say you have a repeated field.

message Foo {
  optional int32 val = 1;
}

message Bar {
  repeated Foo foo = 1;
}

This will generate the method

List<Foo> getFooList()

Is there any circumstance where getFooList will return null? Or will it already return a List, even if it's empty?

Answer 1

No, there is no case where it returns null. In fact, none of the field accessors on Java protobuf generated classes ever return null; they always return the default value if the field is not present. Similarly, the setters do not allow you to set null.

Answer 2

Note that no Java protocol buffer methods accept or return nulls unless otherwise specified.

Reference: https://developers.google.com/protocol-buffers/docs/reference/java-generated

Answer 3

The default value for repeated fields is empty (generally an empty list in the appropriate language).

Source: https://developers.google.com/protocol-buffers/docs/proto3#default