code: public org.grails.datastore.mapping.query.api.Criteria sizeEq(String propertyName, int size) {
          if (!validateSimpleExpression()) {
              throwRuntimeException(new IllegalArgumentException("Call to [sizeEq] with propertyName [" +
                      propertyName + "] and size [" + size + "] not allowed here."));
          }
  
          propertyName = calculatePropertyName(propertyName);
          addToCriteria(Restrictions.sizeEq(propertyName, size));
          return this;
      }
docs: Creates a Criterion that contrains a collection property by size
  
  @param propertyName The property name
  @param size The size to constrain by
  
  @return A Criterion instance