Fix NPE in error message generation and reuse method

h2/src/main/org/h2/command/dml/Insert.java

@@ -305,15 +305,7 @@ public class Insert extends Prepared implements ResultTarget {
                     buff.append(",\n");
                 }
                 buff.append('(');
-                buff.resetCount();
-                for (Expression e : expr) {
-                    buff.appendExceptFirst(", ");
-                    if (e == null) {
-                        buff.append("DEFAULT");
-                    } else {
-                        e.getSQL(buff.builder());
-                    }
-                }
+                Expression.writeExpressions(buff.builder(), expr);
                 buff.append(')');
             }
         } else {

h2/src/main/org/h2/command/dml/Merge.java

@@ -242,15 +242,7 @@ public class Merge extends Prepared {
                     buff.append(", ");
                 }
                 buff.append('(');
-                buff.resetCount();
-                for (Expression e : expr) {
-                    buff.appendExceptFirst(", ");
-                    if (e == null) {
-                        buff.append("DEFAULT");
-                    } else {
-                        e.getSQL(buff.builder());
-                    }
-                }
+                Expression.writeExpressions(buff.builder(), expr);
                 buff.append(')');
             }
         } else {

h2/src/main/org/h2/command/dml/Replace.java

@@ -222,15 +222,7 @@ public class Replace extends Prepared {
                     buff.append(", ");
                 }
                 buff.append('(');
-                buff.resetCount();
-                for (Expression e : expr) {
-                    buff.appendExceptFirst(", ");
-                    if (e == null) {
-                        buff.append("DEFAULT");
-                    } else {
-                        e.getSQL(buff.builder());
-                    }
-                }
+                Expression.writeExpressions(buff.builder(), expr);
                 buff.append(')');
             }
         } else {

h2/src/main/org/h2/expression/Expression.java

@@ -54,7 +54,12 @@ public abstract class Expression {
             if (i > 0) {
                 builder.append(", ");
             }
-            expressions[i].getSQL(builder);
+            Expression e = expressions[i];
+            if (e == null) {
+                builder.append("DEFAULT");
+            } else {
+                e.getSQL(builder);
+            }
         }
     }