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 In jBPM , REST APIs are widely used to start processes, complete tasks, and exchange variables with external systems. A very common production problem is: ❌ jBPM REST API fails due to serialization / deserialization errors (JSON mapping error, empty response, 400/500 error, or variables not persisted correctly) This blog explains the root causes , how to identify the issue , and proven fixes used in real projects. 1️⃣ What Is a Serialization Issue in jBPM REST? Serialization issues occur when: jBPM cannot convert Java objects to JSON or cannot reconstruct Java objects from JSON This typically happens while: Starting a process via REST Completing a human task Passing complex process variables 2️⃣ Most Common Symptoms You may see: HTTP 400 / 500 errors Empty or partial REST responses Exceptions like: Cannot construct instance No serializer found ClassNotFoundException InvalidDefinitionException Process instance starts but variables are missing Task completion fails without clear ...

When working with jBPM REST APIs , one of the most common and frustrating problems developers face is serialization errors while starting a process or passing variables . These issues usually appear only at runtime , often in integration or production environments , making them harder to debug. In this article, we’ll understand: Why jBPM REST serialization issues occur Common error messages Practical solutions that actually work in real projects 🔴 Common Error Messages You may encounter errors like: Cannot find serializer for value 'ObjectValue [...]' or Cannot write serialized value for variable 'body' : no 'objectTypeName' provided for non- null value or Unable to deserialize content as ObjectValue These errors usually happen when: Starting a process instance Completing a task Passing complex JSON or Java objects via REST 🧠 Root Causes (Very Important) 1️⃣ Passing JSON as a Plain String A very common mistake is sending JSON l...