fix(service): add null guard to deleteBySquadNumber (#268)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nanotaboada

src/main/java/ar/com/nanotaboada/java/samples/spring/boot/services/PlayersService.java

@@ -236,6 +236,11 @@ public boolean update(Integer squadNumber, PlayerDTO playerDTO) {
     public boolean deleteBySquadNumber(Integer squadNumber) {
         log.debug("Deleting player with squad number: {}", squadNumber);
 
+        if (squadNumber == null) {
+            log.warn("Cannot delete player - squad number is null");
+            return false;
+        }
+
         return playersRepository.findBySquadNumber(squadNumber)
                 .map(existing -> {
                     playersRepository.deleteById(existing.getId());

src/test/java/ar/com/nanotaboada/java/samples/spring/boot/test/services/PlayersServiceTests.java

@@ -438,4 +438,19 @@ void givenPlayerDoesNotExist_whenDelete_thenReturnsFalse() {
         verify(playersRepositoryMock, never()).deleteById(any());
         then(actual).isFalse();
     }
+
+    /**
+     * Given a null squad number is passed
+     * When deleteBySquadNumber() is called
+     * Then false is returned without hitting the repository
+     */
+    @Test
+    void givenNullSquadNumber_whenDelete_thenReturnsFalse() {
+        // Given / When
+        boolean actual = playersService.deleteBySquadNumber(null);
+        // Then
+        verify(playersRepositoryMock, never()).findBySquadNumber(any());
+        verify(playersRepositoryMock, never()).deleteById(any());
+        then(actual).isFalse();
+    }
 }