fix bug

src/connector/jdbc/src/main/java/com/taosdata/jdbc/TSDBPreparedStatement.java

@@ -14,7 +14,6 @@
  *****************************************************************************/
 package com.taosdata.jdbc;
 
-import com.sun.tools.javac.util.Assert;
 import com.taosdata.jdbc.utils.Utils;
 
 import java.io.InputStream;

src/connector/jdbc/src/main/java/com/taosdata/jdbc/utils/NullType.java

@@ -0,0 +1,55 @@
+package com.taosdata.jdbc.utils;
+
+public class NullType {
+    private static final byte NULL_BOOL_VAL = 0x2;
+    private static final String NULL_STR = "null";
+
+    public String toString() {
+        return NullType.NULL_STR;
+    }
+
+    public static boolean isBooleanNull(byte val) {
+        return val == NullType.NULL_BOOL_VAL;
+    }
+
+    public static boolean isTinyIntNull(byte val) {
+        return val == Byte.MIN_VALUE;
+    }
+
+    public static boolean isSmallIntNull(short val) {
+        return val == Short.MIN_VALUE;
+    }
+
+    public static boolean isIntNull(int val) {
+        return val == Integer.MIN_VALUE;
+    }
+
+    public static boolean isBigIntNull(long val) {
+        return val == Long.MIN_VALUE;
+    }
+
+    public static boolean isFloatNull(float val) {
+        return Float.isNaN(val);
+    }
+
+    public static boolean isDoubleNull(double val) {
+        return Double.isNaN(val);
+    }
+
+    public static boolean isBinaryNull(byte[] val, int length) {
+        if (length != Byte.BYTES) {
+            return false;
+        }
+
+        return val[0] == 0xFF;
+    }
+
+    public static boolean isNcharNull(byte[] val, int length) {
+        if (length != Integer.BYTES) {
+            return false;
+        }
+
+        return (val[0] & val[1] & val[2] & val[3]) == 0xFF;
+    }
+
+}