Simplify the use of the fee extension a little

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=133149148

java/google/registry/model/domain/fee/FeeCheckCommandExtension.java

@@ -24,7 +24,7 @@ import org.joda.money.CurrencyUnit;
  * of items requesting the fees for particular commands and domains. For some versions of the fee
  * extension, the currency is also specified here; for other versions it is contained in the
  * individual items.
- * 
+ *
  * @type C the type of extension item used by this command (e.g. v6 items for a v6 extension)
  * @type R the type of response returned for for this command (e.g. v6 responses for a v6 extension)
  */
@@ -33,13 +33,14 @@ public interface FeeCheckCommandExtension<
         R extends FeeCheckResponseExtension<?>>
     extends CommandExtension {
 
-  /** True if this version of the fee extension specifies the currency at the top level. */
-  public boolean isCurrencySupported();
+  /**
+   * Three-character ISO4217 currency code.
+   *
+   * <p>Returns null if this version of the fee extension doesn't specify currency at the top level.
+   */
+  public CurrencyUnit getCurrency();
 
-  /** Three-character currency code; throws an exception if currency is not supported. */
-  public CurrencyUnit getCurrency() throws UnsupportedOperationException;
-  
   public ImmutableSet<C> getItems();
-    
+
   public R createResponse(ImmutableList<? extends FeeCheckResponseExtensionItem> items);
 }

java/google/registry/model/domain/fee/FeeQueryCommandExtensionItem.java

@@ -35,18 +35,19 @@ public interface FeeQueryCommandExtensionItem {
     UPDATE
   }
 
-  /** True if this version of fee extension includes a currency in this type of query item. */
-  public boolean isCurrencySupported();
-
-  /** A three-character ISO4217 currency code; throws an exception if currency is not supported. */
-  public CurrencyUnit getCurrency() throws UnsupportedOperationException;
+  /**
+   * Three-character ISO4217 currency code.
+   *
+   * <p>Returns null if this version of the fee extension doesn't specify currency at the top level.
+   */
+  public CurrencyUnit getCurrency();
 
   /** The name of the command being checked. */
   public CommandName getCommandName();
-  
+
   /** The unparse name of the command being checked, for use in error strings. */
   public String getUnparsedCommandName();
-  
+
   /** The phase of the command being checked. */
   public String getPhase();
 

java/google/registry/model/domain/fee06/FeeCheckCommandExtensionItemV06.java

@@ -29,7 +29,7 @@ public class FeeCheckCommandExtensionItemV06
   String name;
 
   CurrencyUnit currency;
-  
+
   @Override
   public boolean isDomainNameSupported() {
     return true;
@@ -40,11 +40,6 @@ public class FeeCheckCommandExtensionItemV06
     return name;
   }
 
-  @Override
-  public boolean isCurrencySupported() {
-    return true;
-  }
-
   @Override
   public CurrencyUnit getCurrency() {
     return currency;

java/google/registry/model/domain/fee06/FeeCheckCommandExtensionV06.java

@@ -32,18 +32,13 @@ public class FeeCheckCommandExtensionV06 extends ImmutableObject
     implements FeeCheckCommandExtension<
         FeeCheckCommandExtensionItemV06,
         FeeCheckResponseExtensionV06> {
-  
+
   @XmlElement(name = "domain")
   Set<FeeCheckCommandExtensionItemV06> items;
 
-  @Override
-  public boolean isCurrencySupported() {
-    return false;
-  }
-
   @Override
   public CurrencyUnit getCurrency() {
-    throw new UnsupportedOperationException("Currency not supported");
+    return null;  // This version of the fee extension doesn't specify a top-level currency.
   }
 
   @Override

java/google/registry/model/domain/fee06/FeeInfoCommandExtensionV06.java

@@ -25,15 +25,10 @@ import org.joda.money.CurrencyUnit;
 @XmlType(propOrder = {"currency", "command", "period"})
 public class FeeInfoCommandExtensionV06
     extends FeeQueryCommandExtensionItemImpl implements CommandExtension {
-  
+
   /** A three-character ISO4217 currency code. */
   CurrencyUnit currency;
 
-  @Override
-  public boolean isCurrencySupported() {
-    return true;
-  }
-
   @Override
   public CurrencyUnit getCurrency() {
     return currency;

java/google/registry/model/domain/fee11/FeeCheckCommandExtensionV11.java

@@ -52,22 +52,20 @@ public class FeeCheckCommandExtensionV11 extends ImmutableObject
 
   /** Three-letter currency code in which results should be returned. */
   CurrencyUnit currency;
-  
+
   /** The period to check. */
   Period period;
 
   /** The class to check. */
   @XmlElement(name = "class")
   String feeClass;
-  
-  @Override
-  public boolean isCurrencySupported() {
-    return false;
-  }
-  
+
   @Override
   public CurrencyUnit getCurrency() {
-    throw new UnsupportedOperationException("Currency not supported");
+    // This version of the fee extension does not have any items, and although the currency is
+    // specified at the top level we've modeled it as a single fake item with the currency inside,
+    // so there's no top level currency to return here.
+    return null;  
   }
 
   @Override
@@ -96,13 +94,13 @@ public class FeeCheckCommandExtensionV11 extends ImmutableObject
     public CommandName getCommandName() {
       return command.getCommand();
     }
-  
+
     /** The command name before being parsed into an enum, for use in error strings. */
     @Override
     public String getUnparsedCommandName() {
       return command.getUnparsedCommandName();
     }
-  
+
     /** The phase of the command being checked. */
     @Override
     public String getPhase() {
@@ -119,22 +117,17 @@ public class FeeCheckCommandExtensionV11 extends ImmutableObject
     public Period getPeriod() {
       return Optional.fromNullable(period).or(DEFAULT_PERIOD);
     }
-    
+
     @Override
     public boolean isDomainNameSupported() {
       return false;
     }
-    
+
     @Override
     public String getDomainName() {
       throw new UnsupportedOperationException("Domain not supported");
     }
 
-    @Override
-    public boolean isCurrencySupported() {
-      return true;
-    }
-
     @Override
     public CurrencyUnit getCurrency() {
       return currency;

java/google/registry/model/domain/fee12/FeeCheckCommandExtensionItemV12.java

@@ -30,13 +30,13 @@ import org.joda.time.DateTime;
 /**
  * An individual price check item in version 0.12 of the fee extension on domain check commands.
  * Items look like:
- * 
+ *
  * <fee:command name="renew" phase="sunrise" subphase="hello">
  *   <fee:period unit="y">1</fee:period>
  *   <fee:class>premium</fee:class>
  *   <fee:date>2017-05-17T13:22:21.0Z</fee:date>
  * </fee:command>
- * 
+ *
  * In a change from previous versions of the extension, items do not contain domain names; instead,
  * the names from the non-extension check element are used.
  */
@@ -49,7 +49,7 @@ public class FeeCheckCommandExtensionItemV12
 
   @XmlAttribute(name = "name")
   String commandName;
-  
+
   @XmlAttribute
   String phase;
 
@@ -58,10 +58,10 @@ public class FeeCheckCommandExtensionItemV12
 
   @XmlElement
   Period period;
- 
+
   @XmlElement(name = "class")
   String feeClass;
-  
+
   @XmlElement(name = "date")
   DateTime feeDate;
 
@@ -75,22 +75,17 @@ public class FeeCheckCommandExtensionItemV12
   public String getDomainName() {
     throw new UnsupportedOperationException("Domain not supported");
   }
-  
-  @Override
-  public boolean isCurrencySupported() {
-    return false;
-  }
-  
+
   @Override
   public CurrencyUnit getCurrency() {
-    throw new UnsupportedOperationException("Currency not supported");
+    return null;  // This version of the fee extension doesn't specify currency per-item.
   }
-  
+
   @Override
   public String getUnparsedCommandName() {
     return commandName;
   }
-  
+
   @Override
   public CommandName getCommandName() {
     // Require the xml string to be lowercase.
@@ -108,7 +103,7 @@ public class FeeCheckCommandExtensionItemV12
   public String getPhase() {
     return phase;
   }
-  
+
   @Override
   public String getSubphase() {
     return subphase;

java/google/registry/model/domain/fee12/FeeCheckCommandExtensionV12.java

@@ -36,17 +36,12 @@ public class FeeCheckCommandExtensionV12 extends ImmutableObject
         FeeCheckResponseExtensionV12> {
 
   CurrencyUnit currency;
-  
-  @Override
-  public boolean isCurrencySupported() {
-    return true;
-  }
 
   @Override
   public CurrencyUnit getCurrency() {
     return currency;
   }
-  
+
   @XmlElement(name = "command")
   Set<FeeCheckCommandExtensionItemV12> items;