test: add null-guard and SelectBuilder offset tests for full coverage

Cover the five NullPointerException guards in QueryBuilderDefaults that
were previously unreachable in tests:
  - builder(null) on the static factory
  - Builder.dialect(null)
  - Builder.defaultColumns(null)
  - Builder.likePrefix(null)
  - Builder.likeSuffix(null)

Also add selectBuilderDefaultOffsetApplied to hit the true-branch of the
defaultOffset ternary in SelectBuilder.buildLimitOffsetClause().

QueryBuilderDefaults now reports 100% line coverage; SelectBuilder
reaches 97.7% (only the unreachable UnsupportedOperationException path
for unknown operators remains uncovered).

Author: ez-plugins

src/test/java/com/github/ezframework/javaquerybuilder/query/QueryBuilderDefaultsTest.java

@@ -85,6 +85,35 @@ void setGlobalNullThrowsNullPointerException() {
         assertThrows(NullPointerException.class, () -> QueryBuilderDefaults.setGlobal(null));
     }
 
+    @Test
+    void builderFromNullSourceThrowsNullPointerException() {
+        assertThrows(NullPointerException.class, () -> QueryBuilderDefaults.builder(null));
+    }
+
+    @Test
+    void builderDialectSetToNullThrowsNullPointerException() {
+        assertThrows(NullPointerException.class,
+            () -> QueryBuilderDefaults.builder().dialect(null));
+    }
+
+    @Test
+    void builderDefaultColumnsSetToNullThrowsNullPointerException() {
+        assertThrows(NullPointerException.class,
+            () -> QueryBuilderDefaults.builder().defaultColumns(null));
+    }
+
+    @Test
+    void builderLikePrefixSetToNullThrowsNullPointerException() {
+        assertThrows(NullPointerException.class,
+            () -> QueryBuilderDefaults.builder().likePrefix(null));
+    }
+
+    @Test
+    void builderLikeSuffixSetToNullThrowsNullPointerException() {
+        assertThrows(NullPointerException.class,
+            () -> QueryBuilderDefaults.builder().likeSuffix(null));
+    }
+
     @Test
     void withDefaultsNullThrowsNullPointerExceptionOnQueryBuilder() {
         assertThrows(NullPointerException.class,
@@ -312,6 +341,19 @@ void selectBuilderDefaultLimitApplied() {
             "Expected LIMIT 30: " + result.getSql());
     }
 
+    @Test
+    void selectBuilderDefaultOffsetApplied() {
+        QueryBuilderDefaults defaults = QueryBuilderDefaults.builder()
+            .defaultLimit(10)
+            .defaultOffset(5)
+            .build();
+
+        SqlResult result = new SelectBuilder().withDefaults(defaults).from("users").build();
+
+        assertTrue(result.getSql().contains("OFFSET 5"),
+            "Expected OFFSET 5: " + result.getSql());
+    }
+
     @Test
     void selectBuilderLikeWrapsWithDefaults() {
         QueryBuilderDefaults defaults = QueryBuilderDefaults.builder()