fix: Crashes when records contain static fields (#6095)

Spoon tried to remove the field to prevent record field duplication.
This fails for static fields, which do not exist (yet). For these, spoon
passed null to the remove method, which failed with an exception. We now
check for the modifier and null explicitly.

src/main/java/spoon/support/compiler/jdt/ParentExiter.java

@@ -254,8 +254,11 @@ public <T> void scanCtType(CtType<T> type) {
 		} else if (child instanceof CtField<?> field) {
 			// We add the field in addRecordComponent. Afterward, however, JDT visits the Field itself -> Duplication.
 			// To combat this, we delete the existing field and trust JDTs version.
-			if (type instanceof CtRecord record) {
-				record.removeField(record.getField(field.getSimpleName()));
+			if (type instanceof CtRecord record && !field.isStatic()) {
+				CtField<?> existing = record.getField(field.getSimpleName());
+				if (existing != null) {
+					record.removeField(existing);
+				}
 			}
 			type.addField(field);
 			return;

src/test/java/spoon/test/record/CtRecordTest.java

@@ -24,6 +24,7 @@
 import spoon.reflect.code.CtReturn;
 import spoon.reflect.code.CtStatement;
 import spoon.reflect.declaration.CtAnonymousExecutable;
+import spoon.reflect.declaration.CtClass;
 import spoon.reflect.declaration.CtConstructor;
 import spoon.reflect.declaration.CtElement;
 import spoon.reflect.declaration.CtField;
@@ -315,6 +316,21 @@ void testProperReturnInRecordAccessor(Factory factory) {
 		}
 	}
 
+	@Test
+	void testRecordWithStaticField() {
+		// contract: Static fields in records do not cause crashes
+		CtClass<?> parsed = Launcher.parseClass("""
+			public record User(int id, String name) {
+			  private static String ADMIN_NAME = "admin";
+			}
+			""");
+		assertThat(parsed).isInstanceOf(CtRecord.class);
+		assertThat(parsed).getFields().hasSize(3);
+		assertThat(parsed.getFields()).anySatisfy(it -> assertThat(it.getSimpleName()).isEqualTo("id"));
+		assertThat(parsed.getFields()).anySatisfy(it -> assertThat(it.getSimpleName()).isEqualTo("name"));
+		assertThat(parsed.getFields()).anySatisfy(it -> assertThat(it.getSimpleName()).isEqualTo("ADMIN_NAME"));
+	}
+
 	private <T> T head(Collection<T> collection) {
 		return collection.iterator().next();
 	}