fix NPE

Author: Luro02

src/main/java/spoon/reflect/visitor/filter/PotentialVariableDeclarationFunction.java

@@ -248,7 +248,7 @@ private record VariableScope(CtVariable<?> variable, CtElement element) implemen
 	// the parent `CtBinaryOperator`, the variables introduced by the branch `CtExpression b` will become relevant too.
 	//
 	// The function below can be used to explore the variables introduced by that unexplored branch `CtExpression b`.
-	private static List<Scope> exploreBranchForNewScopes(CtQueryable branch) {
+	private static List<Scope> exploreBranchForNewScopes(@NonNull CtQueryable branch) {
 		List<Scope> result = new ArrayList<>();
 
 		// Where pattern variables apply changes depending on their parents (e.g. !(< pattern >) will change the matches),
@@ -306,14 +306,14 @@ private static List<Scope> exploreBranchForNewScopes(CtQueryable branch) {
 	}
 
 	@SuppressWarnings("unchecked")
-	private static List<PatternScope> exploreBranchForNewPatternScopes(CtExpression<?> branch) {
+	private static List<PatternScope> exploreBranchForNewPatternScopes(@NonNull CtExpression<?> branch) {
 		// SAFETY: In an expression only PatternScope can appear
 		//      -> the returns of exploreBranchForNewScopes is guaranteed to be a list of PatternScope
 		return (List<PatternScope>) (List<?>) exploreBranchForNewScopes(branch);
 	}
 
 	@SuppressWarnings("unchecked")
-	private static List<PatternScope> exploreBranchForNewPatternScopes(CtPattern branch) {
+	private static List<PatternScope> exploreBranchForNewPatternScopes(@NonNull CtPattern branch) {
 		// SAFETY: In a pattern only PatternScope can appear
 		//      -> the returns of exploreBranchForNewScopes is guaranteed to be a list of PatternScope
 		return (List<PatternScope>) (List<?>) exploreBranchForNewScopes(branch);
@@ -577,7 +577,7 @@ private static List<Scope> updatePatternScopesForParent(Collection<PatternScope>
 			return result;
 		}
 
-		if (parent instanceof CtFor ctFor) {
+		if (parent instanceof CtFor ctFor && ctFor.getExpression() != null) {
 			List<Scope> result = new ArrayList<>();
 
 			// The following rules apply to a basic for statement (§14.14.1):

src/test/java/spoon/test/query_function/VariableReferencesTest.java

@@ -588,4 +588,24 @@ public void testIfWithNullThen(@BySimpleName("Test") CtClass<?> ctClass) {
 		// System.out
 		assertThat(references.get(2)).hasExactlyPotentialDeclarations(patternVar, fieldVariable); // println(s)
 	}
+
+	@ModelTest(code = """
+		class Test {
+			void method() {
+				int i = 0;
+				for (; ;) {
+					System.out.println(i);
+				}
+			}
+		}
+		""")
+	public void testForConditionNull(@BySimpleName("Test") CtClass<?> ctClass) {
+		// contract: the code must not crash if the condition in the for is null
+		List<CtVariable<?>> variables = ctClass.getElements(new TypeFilter<>(CtVariable.class));
+		List<CtVariableReference<?>> references = ctClass.getElements(new TypeFilter<>(CtVariableReference.class));
+
+		assertThat(variables).hasSize(1);
+
+		assertThat(references.get(1)).hasExactlyPotentialDeclarations(variables.get(0));
+	}
 }