Write clear FEEL expressions

Common expression shapes

amount < 1000
customer.tier = "gold"
[100..500]
if approved then "continue" else "review"

Know where the expression is used

A decision-table input entry, a gateway condition and a variable mapping may have different wrappers. The leading = is optional on Priostack: amount > 1000 and =amount > 1000 give the same answer. Keep it if the model is also edited in Camunda Modeler, which writes it.

Check boundaries and missing values

Test numbers separately from numeric strings, and include empty lists and threshold values. null equals only null; x != null is true only when x has a value; <, <=, > and >= with null are false. In a gateway condition, a variable that was never set is an error that raises an incident, so set it (to null if need be) before the gateway. In XML, escape the less-than sign before deployment.