Do not create a proxy when ResultSet is null

`Statement.getResultSet` can return `null`.
In that case, do not create a `ResultSet` proxy.

Resolves #117

Author: ttddyy

src/main/java/net/ttddyy/dsproxy/proxy/StatementProxyLogic.java

@@ -293,7 +293,7 @@ protected Object performProxyLogic(Object proxy, Method method, Object[] args, M
             final boolean isResultSetReturningMethod = !isGetGeneratedKeysMethod && METHODS_TO_RETURN_RESULTSET.contains(methodName);
 
             final boolean isCreateGeneratedKeysProxy = isGetGeneratedKeysMethod && this.proxyConfig.isGeneratedKeysProxyEnabled();
-            final boolean isCreateResultSetProxy = isResultSetReturningMethod && this.proxyConfig.isResultSetProxyEnabled();
+            final boolean isCreateResultSetProxy = (retVal != null && isResultSetReturningMethod && this.proxyConfig.isResultSetProxyEnabled());
 
             // create proxy for returned ResultSet
             if (isCreateGeneratedKeysProxy) {

src/main/java/net/ttddyy/dsproxy/proxy/jdk/JdkJdbcProxyFactory.java

@@ -8,7 +8,11 @@
 
 import javax.sql.DataSource;
 import java.lang.reflect.Proxy;
-import java.sql.*;
+import java.sql.CallableStatement;
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.Statement;
 
 /**
  * Dynamic Proxy Class(Jdk Proxy) based {@link net.ttddyy.dsproxy.proxy.JdbcProxyFactory} implementation.

src/test/java/net/ttddyy/dsproxy/proxy/StatementProxyLogicMockTest.java

@@ -808,7 +808,6 @@ public void testEquals() throws Throwable {
 
     @Test
     public void proxyResultSet() throws Throwable {
-
         final AtomicReference<Object> listenerReceivedResult = new AtomicReference<Object>();
         QueryExecutionListener listener = new NoOpQueryExecutionListener() {
             @Override
@@ -817,13 +816,11 @@ public void afterQuery(ExecutionInfo execInfo, List<QueryInfo> queryInfoList) {
             }
         };
 
-
         ResultSetMetaData metaData = mock(ResultSetMetaData.class);
 
         ResultSet resultSet = mock(ResultSet.class);
         when(resultSet.getMetaData()).thenReturn(metaData);
 
-
         Statement stmt = mock(Statement.class);
         when(stmt.executeQuery(anyString())).thenReturn(resultSet);
         when(stmt.getGeneratedKeys()).thenReturn(resultSet);
@@ -859,8 +856,18 @@ public void afterQuery(ExecutionInfo execInfo, List<QueryInfo> queryInfoList) {
         result = logic.invoke(null, getGeneratedKeysMethod, null);
         assertThat(result).isInstanceOf(ResultSet.class);
         assertFalse(Proxy.isProxyClass(result.getClass()));
+    }
 
+    @Test
+    public void resultSetIsNull() throws Throwable {
+        Statement stmt = mock(Statement.class);
+        when(stmt.getResultSet()).thenReturn(null);
+        Method getResultSetMethod = Statement.class.getMethod("getResultSet");
 
+        StatementProxyLogic logic = getProxyLogic(stmt, null, null, true, false);
+        Object result = logic.invoke(null, getResultSetMethod, null);
+
+        assertThat(result).isNull();
     }
 
     @Test