Criteria. Make DnfExpression implement Expressional to better identif…

…y nils

criteria/common/src/org/immutables/criteria/constraints/CriteriaContext.java

@@ -7,7 +7,7 @@
  * Link between front-end (Criteria DSL) and <a href="https://cs.lmu.edu/~ray/notes/ir/">Intermediate Representation</a>
  * (internally known as {@link Expression}).
  */
-public final class CriteriaContext<R> {
+public final class CriteriaContext<R> implements Expressional<R> {
 
   private final CriteriaCreator<R> creator;
   private final DnfExpression expression;
@@ -50,8 +50,9 @@ public CriteriaContext<R> or() {
     return new CriteriaContext<>(Operators.OR, expression, path, creator);
   }
 
+  @Override
   public Expression expression() {
-    return this.expression.simplify();
+    return this.expression.expression();
   }
 
   @SuppressWarnings("unchecked")

criteria/common/src/org/immutables/criteria/constraints/DnfExpression.java

@@ -14,7 +14,7 @@
  *
  *  <p>Example: {@code (A and B or C and D or E)}
  */
-class DnfExpression implements Expression {
+class DnfExpression implements Expressional<DnfExpression>, Expression {
 
   private final List<Expression> conjunctions;
   private final List<Expression> disjunctions;
@@ -31,10 +31,15 @@ static DnfExpression create() {
   @Nullable
   @Override
   public <R, C> R accept(ExpressionBiVisitor<R, C> visitor, @Nullable C context) {
-    return simplify().accept(visitor, context);
+    return expression().accept(visitor, context);
   }
 
-  Expression simplify() {
+  @Override
+  public Expression expression() {
+    return simplify();
+  }
+
+  private Expression simplify() {
     final List<Expression> expressions = new ArrayList<>(disjunctions);
     if (!conjunctions.isEmpty()) {
       expressions.add(Expressions.and(conjunctions));
@@ -43,7 +48,6 @@ Expression simplify() {
     return Expressions.or(expressions);
   }
 
-
   DnfExpression and(Expression expression) {
     Objects.requireNonNull(expression, "expression");
     ImmutableList<Expression> newConjunctions = ImmutableList.<Expression>builder().addAll(conjunctions).add(expression).build();