Add nullability specifiers to the simple sequence of selectors

HTMLKit/CSSSimpleSequence.h

@@ -14,9 +14,9 @@
 
 @interface CSSSimpleSequence : CSSSelector
 
-- (instancetype)initWithType:(CSSTypeSelector *)selector;
-- (instancetype)initWithSelectors:(NSArray *)selectors;
+- (nullable instancetype)initWithType:(nonnull CSSTypeSelector *)selector;
+- (nullable instancetype)initWithSelectors:(nonnull NSArray<id<CSSSimpleSelector>> *)selectors;
 
-- (void)addSelector:(id<CSSSimpleSelector>)selector;
+- (void)addSelector:(nonnull id<CSSSimpleSelector>)selector;
 
 @end

HTMLKit/CSSSimpleSequence.m

@@ -18,7 +18,7 @@
 
 - (instancetype)init
 {
-	return [self initWithSelectors:nil];
+	return [self initWithSelectors:@[]];
 }
 
 - (instancetype)initWithType:(CSSTypeSelector *)selector