Added Conditionals.IsNull. Modified Key() to use IsNull if a null value is

passed in for a column value.

src/java/com/samskivert/jdbc/depot/Key.java

@@ -22,8 +22,10 @@ package com.samskivert.jdbc.depot;
 
 import com.samskivert.jdbc.depot.clause.Where;
 import com.samskivert.jdbc.depot.expression.ColumnExp;
+import com.samskivert.jdbc.depot.expression.LiteralExp;
 import com.samskivert.jdbc.depot.expression.ValueExp;
 import com.samskivert.jdbc.depot.operator.Conditionals.Equals;
+import com.samskivert.jdbc.depot.operator.Conditionals.IsNull;
 import com.samskivert.jdbc.depot.operator.Logic.And;
 import com.samskivert.jdbc.depot.operator.SQLOperator;
 
@@ -80,7 +82,8 @@ public class Key extends Where
     {
         SQLOperator[] comparisons = new Equals[columns.length];
         for (int ii = 0; ii < columns.length; ii ++) {
-            comparisons[ii] = new Equals(columns[ii], new ValueExp(values[ii]));
+            comparisons[ii] = (values[ii] == null) ?
+                new IsNull(columns[ii]) : new Equals(columns[ii], new ValueExp(values[ii]));
         }
         return new And(comparisons);
     }

src/java/com/samskivert/jdbc/depot/operator/Conditionals.java

@@ -35,6 +35,37 @@ import com.samskivert.jdbc.depot.expression.ValueExp;
  */
 public abstract class Conditionals
 {
+    /** The SQL 'is null' operator. */
+    public static class IsNull
+        implements SQLOperator
+    {
+        public IsNull (Class pClass, String pColumn)
+        {
+            this(new ColumnExp(pClass, pColumn));
+        }
+
+        public IsNull (ColumnExp column)
+        {
+            _column = column;
+        }
+
+        // from SQLExpression
+        public void appendExpression (Query query, StringBuilder builder)
+        {
+            _column.appendExpression(query, builder);
+            builder.append(" is null");
+        }
+
+        // from SQLExpression
+        public int bindArguments (PreparedStatement pstmt, int argIdx)
+            throws SQLException
+        {
+            return argIdx;
+        }
+
+        protected ColumnExp _column;
+    }
+
     /** The SQL '=' operator. */
     public static class Equals extends BinaryOperator
     {