You are a fault localization tool, your task is find the potential buggy lines in the given method.
The bug triggered by this test org.apache.commons.lang3.builder.ToStringBuilderTest::testReflectionCharArray on this test line validateNullToStringStyleRegistry(); with the following error message: junit.framework.AssertionFailedError: Expected: <null> but was: {}
This is the methods convered by the test case.
//method 1
static boolean isRegistered(Object value) {
        Map<Object, Object> m = getRegistry();
        return m.containsKey(value);
    }
//method2
static Map<Object, Object> getRegistry() {
       return REGISTRY.get() != null ? REGISTRY.get() : Collections.<Object, Object>emptyMap();
  }
//method3
static void register(Object value) {
        if (value != null) {
            WeakHashMap<Object, Object> m;
            synchronized (ToStringStyle.class) {
                m = REGISTRY.get();
                if (m == null) {
                    m = new WeakHashMap<Object, Object>();
                    REGISTRY.set(m);
                }
            }
            m.put(value, null);
        }
    }

//method4
static void unregister(Object value) {
        if (value != null) {
            WeakHashMap<Object, Object> m;
            synchronized (ToStringStyle.class) {
                m = REGISTRY.get();
                if (m != null) {
                    m.remove(value);
                    if (m.isEmpty()) {
                        REGISTRY.remove();
                    }
                }
            }
        }
    }

//method5
public void appendStart(StringBuffer buffer, Object object) {
        if (object != null) {
            appendClassName(buffer, object);
            appendIdentityHashCode(buffer, object);
            appendContentStart(buffer);
            if (fieldSeparatorAtStart) {
                appendFieldSeparator(buffer);
            }
        }
    }

Please given me the potential buggy lines according the context provided. You should make your response concise and precise.