DataWeave 2.1 is compatible with Mule 4.1. Standard Support for Mule 4.1 ended on November 2, 2020, and this version of Mule will reach its End of Life on November 2, 2022, when Extended Support ends.

Deployments of new applications to CloudHub that use this version of Mule are no longer allowed. Only in-place updates to applications are permitted.

MuleSoft recommends that you upgrade to the latest version of Mule 4 that is in Standard Support so that your applications run with the latest fixes and security enhancements.

fail(String): Nothing

Produces a failure with the specified message.


Name Description


An error message (String).


This example returns a failure message Data was empty instead of the desiredResult ([1,2,3]) because the expression (sizeOf(emptyArray) ⇐ 0) is true.


%dw 2.0
import * from dw::Runtime
var emptyArray = []
var desiredResult = [1,2,3]
output application/json
if(sizeOf(emptyArray) <= 0) fail('Data was empty') else desiredResult


Data was empty
  at fail (Unknown)
  at main (line: 6, column: 25)

In the Studio console component, the output looks something like this:

ERROR 2018-07-29 11:47:44,983 ...
Message               : "Data was empty

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