Fix gh-11740: Add missing null check in validateProfileId()

The validateProfileId() method was missing a null check before calling
validProfileIds.contains(id). Since validProfileIds uses
ConcurrentHashMap.newKeySet() which doesn't allow null keys, a null
profile ID would cause a NullPointerException instead of a proper
validation error.

This makes validateProfileId() consistent with validateCoordinateId()
which already has the null check.

Fixes #11740

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: abhu85

impl/maven-impl/src/main/java/org/apache/maven/impl/model/DefaultModelValidator.java

@@ -1792,7 +1792,7 @@ private boolean validateProfileId(
             String id,
             @Nullable SourceHint sourceHint,
             InputLocationTracker tracker) {
-        if (validProfileIds.contains(id)) {
+        if (id != null && validProfileIds.contains(id)) {
             return true;
         }
         if (!validateStringNotEmpty(prefix, fieldName, problems, severity, version, id, sourceHint, tracker)) {