Support multiple versions of the EPP Fee Extension

We want to support multiple versions of the fee extension, to allow new features while maintaining backward compatibility. This CL extends the framework and adds one new version, 0.11 (spec version 7), to the existing version 0.6 (spec version 3). A follow-on CL will add version 0.12 (spec version 8).

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127849044

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

@@ -0,0 +1,98 @@
+// Copyright 2016 The Domain Registry Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.model.domain.fee;
+
+import static google.registry.util.CollectionUtils.forceEmptyToNull;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.Buildable.GenericBuilder;
+import google.registry.model.ImmutableObject;
+import google.registry.model.domain.Period;
+import google.registry.model.domain.fee.FeeQueryCommandExtensionItem.CommandName;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
+import javax.xml.bind.annotation.XmlTransient;
+
+/**
+ * Abstract base class for the fee request query items used in Check and Info responses. It handles
+ * command, period, fees and class, which are always present. Derived classes must handle currency,
+ * which may or may not be present, depending on the version of the extension being used.
+ */
+@XmlTransient
+public class FeeQueryResponseExtensionItemImpl
+    extends ImmutableObject implements FeeQueryResponseExtensionItem {
+
+  /** The command that was checked. */
+  FeeExtensionCommandDescriptor command;
+
+  /** The period that was checked. */
+  Period period;
+
+  /**
+   * The magnitude of the fee, in the specified units, with an optional description.
+   *
+   * <p>This is a list because a single operation can involve multiple fees.
+   */
+  List<Fee> fee;
+
+  /**
+   * The type of the fee.
+   *
+   * <p>We will use "premium" for fees on premium names, and omit the field otherwise.
+   */
+  @XmlElement(name = "class")
+  String feeClass;
+
+  @Override
+  public String getFeeClass() {
+    return feeClass;
+  }
+
+  /** Abstract builder for {@link FeeQueryResponseExtensionItemImpl}. */
+  public abstract static class
+      Builder<T extends FeeQueryResponseExtensionItemImpl, B extends Builder<?, ?>>
+          extends GenericBuilder<T, B> implements FeeQueryResponseExtensionItem.Builder {
+    
+    @Override
+    public B setCommand(CommandName commandName, String phase, String subphase) {
+      getInstance().command = FeeExtensionCommandDescriptor.create(commandName, phase, subphase);
+      return thisCastToDerived();
+    }
+
+    @Override
+    public B setPeriod(Period period) {
+      getInstance().period = period;
+      return thisCastToDerived();
+    }
+
+    @Override
+    public B setFees(List<Fee> fees) {
+      // If there are no fees, set the field to null to suppress the 'fee' section in the xml.
+      getInstance().fee = forceEmptyToNull(ImmutableList.copyOf(fees));
+      return thisCastToDerived();
+    }
+
+    public B setFee(List<Fee> fees) {
+      getInstance().fee = forceEmptyToNull(ImmutableList.copyOf(fees));
+      return thisCastToDerived();
+    }
+
+    @Override
+    public B setClass(String feeClass) {
+      getInstance().feeClass = feeClass;
+      return thisCastToDerived();
+    }
+  }
+}