public Optional<String> messageExpression() {
        return Optional.ofNullable(this.messageExpression);
    }
@return messageExpression declares a CEL expression that evaluates to the validation failure message that is returned when this rule fails. Since messageExpression is used as a failure message, it must evaluate to a string. If both message and messageExpression are present on a validation, then messageExpression will be used if validation fails. If messageExpression results in a runtime error, the runtime error is logged, and the validation failure message is produced as if the messageExpression field were unset. If messageExpression evaluates to an empty string, a string with only spaces, or a string that contains line breaks, then the validation failure message will also be produced as if the messageExpression field were unset, and the fact that messageExpression produced an empty string/string with only spaces/string with line breaks will be logged. messageExpression has access to all the same variables as the `expression` except for &#39;authorizer&#39; and &#39;authorizer.requestResource&#39;. Example: &#34;object.x must be less than max (&#34;+string(params.max)+&#34;)&#34;
sdk/java/src/main/java/com/pulumi/kubernetes/admissionregistration/v1beta1/outputs/ValidationPatch.java