Allow empty <developers/> and <contributors/>

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@321282 13f79535-47bb-0310-9956-ffa450edef68

pom/src/plugin-resources/xsd/pom-strict-3.xsd

@@ -294,7 +294,7 @@
 
         <xs:complexType>
           <xs:sequence>
-            <xs:element maxOccurs="unbounded" name="developer"
+            <xs:element minOccurs="0" maxOccurs="unbounded" name="developer"
                         type="Developer"/>
           </xs:sequence>
         </xs:complexType>
@@ -312,7 +312,7 @@
 
         <xs:complexType>
           <xs:sequence>
-            <xs:element maxOccurs="unbounded" name="contributor"
+            <xs:element minOccurs="0" maxOccurs="unbounded" name="contributor"
                         type="Contributor"/>
           </xs:sequence>
         </xs:complexType>