ModifiedButNotUsed
A collection or proto builder was created, but its values were never accessed.

Severity
WARNING
Has Fix?
REQUIRES_HUMAN_ATTENTION

The problem

Collections and proto builders which are created and mutated but never used may be a sign of a bug, for example:

```java {.bad} MyProto.Builder builder = MyProto.newBuilder(); if (field != null) { MyProto.NestedField.Builder nestedBuilder = MyProto.NestedField.newBuilder(); nestedBuilder.setValue(field); // Oops–forgot to do anything with nestedBuilder. } return builder.build();


Likewise, converting a proto to a builder and modifying it is a no-op unless
something is done with the return value:

```java {.bad}
  void setFoo(MyProto proto, String foo) {
    proto.toBuilder().setFoo(foo).build();
  }

As protos are immutable, either the return value must be used:

```java {.good} @CheckReturnValue MyProto withFoo(MyProto proto, String foo) { return proto.toBuilder().setFoo(foo).build(); }


or the Builder modified in place:

```java {.good}
  void setFoo(MyProto.Builder protoBuilder, String foo) {
    protoBuilder.setFoo(foo);
  }

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("ModifiedButNotUsed") to the enclosing element.