/**
     * This default mode for combining a DOM node during merge means that where element names match, the process will
     * try to merge the element attributes and values, rather than overriding the recessive element completely with the
     * dominant one. This means that wherever the dominant element doesn't provide the value or a particular attribute,
     * that value or attribute will be set from the recessive DOM node.

                for (PluginExecution element : tgt) {
                    Object key = getPluginExecutionKey().apply(element);
                    merged.put(key, element);
                }

                for (PluginExecution element : src) {
                    Object key = getPluginExecutionKey().apply(element);
                    PluginExecution existing = merged.get(key);

     * If {@code element} is not {@code null}, child configuration element with the specified name will
     * be unmarshalled.
     *
     * @param configuration The configuration to unmarshal, may be {@code null}.
     * @param element Configuration element name to unmarshal or {@code null} to unmarshal entire configuration.

 In order the understand how inheritance works in Maven there are a few notions that you must be familiar with:

 * The maven super model

 * how parent poms are processed

 * the order in which elements in the POM are overridden

 * minimum element-set for a valid project pom


Maven super model

 Inheritance is recursive in Maven but there is a special model which is the implicit super parent in the lineage
 of models you may specify:

            <p>By default, every element content is trimmed, but starting with Maven 3.1.0, you can add
            {@code xml:space="preserve"} to elements you want to preserve whitespace.</p>
            <p>You can control how child POMs inherit configuration from parent POMs by adding {@code combine.children}
            or {@code combine.self} attributes to the children of the configuration element:</p>
            <ul>

    </default>
  </defaults>
  <classes>
    <class rootElement="true" xml.tagName="extension">
      <name>ExtensionDescriptor</name>
      <version>1.0.0</version>
      <description><![CDATA[Root element of the <code>extension.xml</code> file.]]></description>
      <fields>
        <field>
          <name>exportedPackages</name>
          <version>1.0.0</version>
          <association>
            <type>String</type>

  <name>Maven Integration Test :: MNG-3979</name>
  <description>
    Test that during inheritance the merging/joining of subtrees with equal identifier doesn't crash if the parent
    POM has a non-empty element and the child POM has an empty element to join.
  </description>

  <properties>
    <prop0>test</prop0>
  </properties>

  <repositories>
    <repository>
      <id>equal-repo-id</id>

import org.apache.maven.api.annotations.Nonnull;

/**
 * Information about the modules contained in a path element.
 * The path element may be a JAR file or a directory. Directories may use either package hierarchy
 * or module hierarchy, but not module source hierarchy. The latter is excluded because this class
 * is for path elements of compiled codes.
 */
class PathModularization {
    /**

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * The annotated element must not be null.
 * <p>
 * Annotated fields must not be null after construction has completed.
 * <p>
 * When this annotation is applied to a method it applies to the method return value.
 *
 * @see Nullable

 */
package org.apache.maven.api.annotations;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * The annotated element can be {@code null}.
 *
 * @see Nonnull
 * @since 4.0.0
 */
@Experimental
@Documented
@Retention(RetentionPolicy.CLASS)