Fix failing tests in JsonMapConverter - Issue #30

[marko-kriskovic]

Summary

This PR fixes the failing JUnit tests in JsonMapConverterTest by correcting an inverted null check condition in the mapToJson method.

Problem

The mapToJson method in JsonMapConverter.java had a logic error on line 42:

if (map != null) {
    throw new IllegalArgumentException("Map cannot be null");
}

This condition was backwards - it was throwing an exception when the map was not null, which caused all tests that passed valid maps to fail.

Solution

Changed the condition to correctly check for null:

if (map == null) {
    throw new IllegalArgumentException("Map cannot be null");
}

Tests Affected

This fix resolves the following failing tests:

• testMapToJson_SimpleMap
• testMapToJson_NestedMap
• testMapToJson_EmptyMap
• testMapToJson_NullInput
• testRoundTrip_JsonToMapToJson

All tests should now pass successfully.

Fixes #30