Summary

Port the null-safe navigation operator (?.) from main branch to ognl-3-4-x branch, enabling safer null handling for Java 8 users.

Key Features:

• New ?. operator for null-safe property navigation
• Returns null instead of throwing exceptions when encountering null intermediate values
• Fully backward compatible with existing OGNL expressions
• 100% Java 8 compatible (no Java 9+ features)

Ported from:

• PR feat: implement null-safe navigation operator (.?) #484 (initial implementation)
• PR refactor: change null-safe operator syntax from .? to ?. #496 (refactoring and standardization)

Changes

Grammar/Parser (src/main/javacc/ognl.jj)

• Added SAFE_DOT token for ?. operator
• Modified navigationChain() production rule to detect and flag null-safe navigation

Core Implementation (src/main/java/ognl/ASTChain.java)

• Added nullSafe field with getter/setter
• Updated getValueBody() to return null on encountering null intermediate values
• Modified toString() to output ?. when nullSafe is true
• Added shouldAppendNavigationOperator() helper method

Test Suite (61+ tests)

• NullSafeOperatorTest.java - 26 tests for basic functionality
• NullSafeCollectionTest.java - 13 tests for collections
• NullSafeCompilationTest.java - 6 tests for compilation
• NullSafeIntegrationTest.java - 16 tests for edge cases

Examples

// Basic null-safe navigation
user?.profile?.city              // Returns null if any part is null

// Method calls
user?.getProfile()?.getBio()     // Returns null if any part is null

// Collections
users?.{name}                    // Returns null if users is null
users?.{? #this.age > 18}        // Returns null if users is null

// Variables
#myVar?.someProperty              // Returns null if #myVar is null

// Mixed safe/unsafe
user.profile?.address.city       // Flexible combination

Test Results

✅ All 947 tests pass (including 61+ new null-safe operator tests)

Tests run: 947, Failures: 0, Errors: 0, Skipped: 0

Differences from Main Branch

• No shortCircuit logic: The ognl-3-4-x branch doesn't have the shortCircuit system property, so that logic was intentionally skipped
• Java 8 compatible: Uses Arrays.asList() instead of List.of(), traditional casting instead of pattern matching
• Backward compatible: All existing tests pass without modification

Test Plan

• All existing tests pass (947 tests)
• New null-safe operator tests pass (61+ tests)
• Parser successfully recognizes ?. syntax
• Null-safe navigation returns null on encountering null values
• toString() correctly outputs ?. operator
• Backward compatibility verified (existing expressions unchanged)
• Java 8 compatibility verified (no Java 9+ APIs used)

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