message: Allowing sqlExpression to be blank
diff: @@ -45,7 +45,8 @@ export default class AdhocFilter {
  this.clause = adhocFilter.clause;
  this.sqlExpression = null;
  } else if (this.expressionType === EXPRESSION_TYPES.SQL) {
  - this.sqlExpression = adhocFilter.sqlExpression ||
  + this.sqlExpression = typeof adhocFilter.sqlExpression === 'string' ?
  + adhocFilter.sqlExpression :
  translateToSql(adhocFilter, { useSimple: true });
  this.clause = adhocFilter.clause;
  this.subject = null;
  