LenientMode not respected when accessing structure fields

[AranyaniSharma]

Description

The lenientMode configuration option is not properly respected when accessing structure fields in expressions. When lenientMode(true) is configured, accessing a missing field in a structure or accessing a property on NULL_VALUE still throws an EvaluationException instead of gracefully returning NULL_VALUE.

Environment

• EvalEx Version: 3.6.0

Expected Behavior

When lenientMode is enabled:

• Accessing a missing field in a structure should return NULL_VALUE instead of throwing an exception
• Accessing a property on NULL_VALUE should return NULL_VALUE instead of throwing an exception

Actual Behavior

The evaluateStructureSeparator() method in Expression.java always throws exceptions for:

1. Missing fields: Field 'xyz' not found in structure
2. Property access on null: Unsupported data types in operation

Even when configuration.isLenientMode() returns true.

Example Code to Reproduce

ExpressionConfiguration config = ExpressionConfiguration.builder()
.lenientMode(true)
.build();

Map<String, Object> data = new HashMap<>();

Expression expression = new Expression("user.name", config);
EvaluationValue result = expression.evaluate(); // Throws exception instead of returning NULL

[AranyaniSharma]

Root Cause

The evaluateStructureSeparator() method in Expression.java (lines ~220-235) does not check configuration.isLenientMode() before throwing exceptions.

Impact

This prevents using EvalEx for null-safe navigation in expressions where nested data structures might have missing or null values, which is a common use case in:

• Data processing pipelines with optional/nullable fields
• JSON/REST API response processing
• Dynamic configuration evaluation
• Any scenario where graceful fallback is needed

Proposed Fix

Modify the evaluateStructureSeparator() method in Expression.java to check lenientMode before throwing exceptions:

private EvaluationValue evaluateStructureSeparator(ASTNode startNode, int depth)
throws EvaluationException {
EvaluationValue structure = evaluateSubtree(startNode.getParameters().get(0), depth + 1);
Token nameToken = startNode.getParameters().get(1).getToken();
String name = nameToken.getValue();

if (structure.isStructureValue()) {
if (!structure.getStructureValue().containsKey(name)) {
// FIX: Check lenientMode before throwing exception for missing field
if (configuration.isLenientMode()) {
return EvaluationValue.NULL_VALUE;
}
throw new EvaluationException(
nameToken, String.format("Field '%s' not found in structure", name));
}
return structure.getStructureValue().get(name);
} else if (structure.isNullValue() && configuration.isLenientMode()) {
// FIX: In lenient mode, allow property access on NULL (returns NULL)
return EvaluationValue.NULL_VALUE;
} else {
throw EvaluationException.ofUnsupportedDataTypeInOperation(startNode.getToken());
}
}

[oswaldobapvicjr]

Hello @AranyaniSharma. Thank you for opening the issue and also suggesting a fix proposal.
I opened PR #558 with the fix and a couple of unit tests.

[oswaldobapvicjr]

Hello @AranyaniSharma. Issue fixed in EvalEx 3.6.1.
Please validate the fix and close the issue.