public Builder op(final Op op) {
            Objects.requireNonNull(op, "Attempt to set null operation");
            this.op = op;
            return this;
        }
Changes the operator of this builder

@param op The operator to set for this builder
@return The {@link Builder}, enabling method chaining
stroom-legacy/stroom-legacy-model_6_1/src/main/java/stroom/legacy/model_6_1/ExpressionOperator.java