[maven-4.0.x] ProtoSession.Builder.newBuilder() NPE on unset property maps

[elharo]

ProtoSession.Builder.newBuilder() NPE on unset property maps

Found in: maven-4.0.x branch
File: api/maven-api-core/src/main/java/org/apache/maven/api/ProtoSession.java (inner class Builder, lines ~110-112, 147-148)
Severity: Low

Description

The newBuilder() factory method creates a Builder without setting userProperties or systemProperties, leaving them as null:

static Builder newBuilder() {
    return new Builder().withStartTime(MonotonicClock.now());
}

// Builder fields are not initialized:
private Map<String, String> userProperties;     // null
private Map<String, String> systemProperties;   // null

public ProtoSession build() {
    return new Impl(userProperties, systemProperties, startTime, topDirectory, rootDirectory);
    // Map.copyOf(null) throws NPE
}

build() passes them to the Impl constructor which calls Map.copyOf(null) on each, resulting in a NullPointerException. The newBuilder() static factory is a public API that leads to an NPE when build() is called without setting properties. Fix by initializing fields to Map.of().