fixes #1177 Calling TypeHandlerRegistry#hasTypeHandler() prevents subsequent regiser() from working properly.

Author: harawata

src/main/java/org/apache/ibatis/type/TypeHandlerRegistry.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2017 the original author or authors.
+ *    Copyright 2009-2018 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -48,7 +48,7 @@ public final class TypeHandlerRegistry {
   private final TypeHandler<Object> UNKNOWN_TYPE_HANDLER = new UnknownTypeHandler(this);
   private final Map<Class<?>, TypeHandler<?>> ALL_TYPE_HANDLERS_MAP = new HashMap<Class<?>, TypeHandler<?>>();
 
-  private static final Map<JdbcType, TypeHandler<?>> NULL_TYPE_HANDLER_MAP = new HashMap<JdbcType, TypeHandler<?>>();
+  private static final Map<JdbcType, TypeHandler<?>> NULL_TYPE_HANDLER_MAP = Collections.emptyMap();
 
   private Class<? extends TypeHandler> defaultEnumTypeHandler = EnumTypeHandler.class;
 
@@ -354,7 +354,7 @@ public <T> void register(Class<T> type, JdbcType jdbcType, TypeHandler<? extends
   private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {
     if (javaType != null) {
       Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.get(javaType);
-      if (map == null) {
+      if (map == null || map == NULL_TYPE_HANDLER_MAP) {
         map = new HashMap<JdbcType, TypeHandler<?>>();
         TYPE_HANDLER_MAP.put(javaType, map);
       }

src/test/java/org/apache/ibatis/type/TypeHandlerRegistryTest.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2017 the original author or authors.
+ *    Copyright 2009-2018 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -206,4 +206,12 @@ public void demoTypeHandlerForSuperInterface() {
     assertSame(SomeInterfaceTypeHandler.class, typeHandlerRegistry.getTypeHandler(ExtendingSomeEnum.class).getClass());
     assertSame(SomeInterfaceTypeHandler.class, typeHandlerRegistry.getTypeHandler(ImplementingMultiInterfaceSomeEnum.class).getClass());
   }
+
+  @Test
+  public void shouldRegisterReplaceNullMap() {
+    class Address {}
+    assertFalse(typeHandlerRegistry.hasTypeHandler(Address.class));
+    typeHandlerRegistry.register(Address.class, StringTypeHandler.class);
+    assertTrue(typeHandlerRegistry.hasTypeHandler(Address.class));
+  }
 }