What causes "'value' property required for " in projectlombok/lombok?

Add a `value` attribute to every nested ` ` element, e.g. ` `

projectlombok/lombok · error · BuildException

'value' property required for

Error message

'value' property required for <format>

What it means

The Ant DelombokTask copies its `<format>` nested elements into the underlying DelombokTaskImpl via reflection. Each nested `<format>` element must carry a `value` attribute; if it is null, the task aborts with a BuildException before running delombok.

Solutions

Add a `value` attribute to every nested `<format>` element, e.g. `<format name="indent" value="4"/>`
Remove `<format>` elements that have no value
Run `java -jar lombok.jar --format-help` to see valid name/value pairs

Example fix

<!-- before -->
<delombok to="build/delomboked">
  <format name="indent"/>
</delombok>
<!-- after -->
<delombok to="build/delomboked">
  <format name="indent" value="tab"/>
</delombok>

Defensive patterns

Strategy: validation

Validate before calling

for (Format f : formatOptions) {
    if (f.getValue() == null) throw new BuildException("<format> needs a value attribute");
}

Try / catch

// BuildException from Ant task execute(); catch in a custom task wrapper if embedding
catch (BuildException e) { if (e.getMessage().contains("'value' property")) { /* fix build.xml */ } throw e; }

Prevention

Always pair name and value in <format> elements
Validate build.xml with a schema or smoke-run the target in CI
Lint for empty attributes in Ant files

When it happens

Trigger: An Ant build.xml contains `<format name="indent"/>` (or `<format value="4"/>` without a name) inside `<delombok>`, so `Format.getValue()` returns null while `execute()` copies formatOptions.

Common situations: Hand-edited Ant scripts omitting `value`; copy-pasting `<format>` elements and deleting the value attribute; relying on a default that does not exist (format options have no defaults in the Ant task).

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of projectlombok/lombok@6d6a3e9fec (2026-09-07). Data as JSON: /api/errors/e5aa961e8196d12b. Report an issue: GitHub.

Appendix: source

Thrown at src/delombok/lombok/delombok/ant/DelombokTask.java:201

				if (t instanceof Error) throw (Error) t;
				throw new RuntimeException(t);
			}
		}
		
		@Override
		public void execute() throws BuildException {
			Location loc = getLocation();
			
			try {
				Object instance = shadowLoadClass("lombok.delombok.ant.DelombokTaskImpl").getConstructor().newInstance();
				for (Field selfField : getClass().getDeclaredFields()) {
					if (selfField.isSynthetic() || Modifier.isStatic(selfField.getModifiers())) continue;
					Field otherField = instance.getClass().getDeclaredField(selfField.getName());
					otherField.setAccessible(true);
					if (selfField.getName().equals("formatOptions")) {
						List<String> rep = new ArrayList<String>();
						for (Format f : formatOptions) {
							if (f.getValue() == null) throw new BuildException("'value' property required for <format>");
							rep.add(f.getValue());
						}
						otherField.set(instance, rep);
					} else {
						otherField.set(instance, selfField.get(this));
					}
				}
				
				Method m = instance.getClass().getMethod("execute", Location.class);
				m.invoke(instance, loc);
			} catch (Throwable t) {
				if (t instanceof InvocationTargetException) t = t.getCause();
				if (t instanceof RuntimeException) throw (RuntimeException) t;
				if (t instanceof Error) throw (Error) t;
				throw new RuntimeException(t);
			}
		}
	}

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