public final NumberExpression<Integer> size() {
        if (size == null) {
            size = Expressions.numberOperation(Integer.class, Ops.MAP_SIZE, mixin);
        }
        return size;
    }
Create a {@code this.size()} expression

@return this.size()
querydsl-core/src/main/java/com/querydsl/core/types/dsl/MapExpressionBase.java