Returns an immutable instance of [FeedbackFormula].
public FeedbackFormula build()Returns an immutable instance of [FeedbackFormula]. Further updates to this [Builder] will not mutate the returned instance. The following fields are required:
.id()
.aggregationType()
.createdAt()
.feedbackKey()
.formulaParts()
.modifiedAt()IllegalStateException: if any required field is unset.