Report a better error message if a bogus rename is attempted. Some formatting

cleanup.

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

@@ -101,9 +101,15 @@ public abstract class EntityMigration extends Modifier
             return true;
         }
 
-        @Override protected void init (String tableName, Map<String,FieldMarshaller<?>> marshallers) {
+        @Override
+        protected void init (String tableName, Map<String, FieldMarshaller<?>> marshallers) {
             super.init(tableName, marshallers);
-            _newColumnDef = marshallers.get(_newColumnName).getColumnDefinition();
+            FieldMarshaller<?> fm = marshallers.get(_newColumnName);
+            if (fm == null) {
+                throw new IllegalArgumentException(
+                    _tableName + " does not contain '" + _newColumnName + "' field.");
+            }
+            _newColumnDef = fm.getColumnDefinition();
         }
 
         protected String _oldColumnName,  _newColumnName;
@@ -133,7 +139,8 @@ public abstract class EntityMigration extends Modifier
             return false;
         }
 
-        @Override protected void init (String tableName, Map<String,FieldMarshaller<?>> marshallers) {
+        @Override
+        protected void init (String tableName, Map<String, FieldMarshaller<?>> marshallers) {
             super.init(tableName, marshallers);
             _columnName = marshallers.get(_fieldName).getColumnName();
             _newColumnDef = marshallers.get(_fieldName).getColumnDefinition();
@@ -174,7 +181,7 @@ public abstract class EntityMigration extends Modifier
      * migration has been determined to be runnable so one cannot rely on this method having been
      * called in {@link #shouldRunMigration}.
      */
-    protected void init (String tableName, Map<String,FieldMarshaller<?>> marshallers)
+    protected void init (String tableName, Map<String, FieldMarshaller<?>> marshallers)
     {
         _tableName = tableName;
     }