void put(R row, C column, V value, BinaryOperator<V> merger) {
      MutableCell<R, C, V> oldCell = table.get(row, column);
      if (oldCell == null) {
        MutableCell<R, C, V> cell = new MutableCell<>(row, column, value);
        insertionOrder.add(cell);
        table.put(row, column, cell);
      } else {
        oldCell.merge(value, merger);
      }
    }

    /*

    void put(R row, C column, V value, BinaryOperator<V> merger) {
      MutableCell<R, C, V> oldCell = table.get(row, column);
      if (oldCell == null) {
        MutableCell<R, C, V> cell = new MutableCell<>(row, column, value);
        insertionOrder.add(cell);
        table.put(row, column, cell);
      } else {
        oldCell.merge(value, merger);
      }
    }

    /*

                    PluginExecution existing = merged.get(key);
                    if (existing != null) {
                        mergePluginExecution(existing, element, sourceDominant, context);
                    } else {
                        merged.put(key, element.clone());
                    }
                }

                target.setExecutions(new ArrayList<>(merged.values()));
            }
        }

class MavenToolchainMergerTest {
    private MavenToolchainMerger merger = new MavenToolchainMerger();

    private DefaultToolchainsReader reader = new DefaultToolchainsReader();

    @Test
    void testMergeNulls() {
        merger.merge(null, null, null);

        PersistedToolchains pt = new PersistedToolchains();
        merger.merge(pt, null, null);
        merger.merge(null, pt, null);
    }

    @Test

import org.apache.maven.model.merge.MavenModelMerger;
import org.codehaus.plexus.util.StringUtils;

/**
 * Handles normalization of a model.
 *
 * @deprecated use {@code org.apache.maven.api.services.ModelBuilder} instead
 */
@Named
@Singleton
@Deprecated(since = "4.0.0")
public class DefaultModelNormalizer implements ModelNormalizer {

    private DuplicateMerger merger = new DuplicateMerger();

    @Override

 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/**
 * POM merger.
 */

@Deprecated(since = "4.0.0")
public class DefaultDependencyManagementInjector implements DependencyManagementInjector {

    private ManagementModelMerger merger = new ManagementModelMerger();

    @Override
    public void injectManagement(Model model, ModelBuildingRequest request, ModelProblemCollector problems) {
        merger.mergeManagedDependencies(model);
    }

    /**
     * ManagementModelMerger
     */

 The following are generated from this model:

   * {{{./apidocs/index.html}Java sources}} with Reader and Writers for the Xpp3 XML parser, <<<ToAPiV3()>>> and <<<ToApiV4()>>> transformers, and <<<v4>>> package
     for Merger and v4 Reader and Writers for the Xpp3 XML parser,

   * A {{{../../api/maven-api-settings/settings.html}Descriptor Reference}}

   * An {{{https://maven.apache.org/xsd/settings-2.0.0.xsd}XSD}}

 The following are generated from this model:

   * {{{./apidocs/index.html}Java sources}} with Reader and Writers for the Xpp3 XML parser, <<<ToAPiV3()>>> and <<<ToApiV4()>>> transformers, and <<<v4>>> package
     for Merger and v4 Reader and Writers for the Xpp3 XML parser,

   * A {{{../../api/maven-api-toolchain/toolchains.html}Descriptor Reference}}

                    PluginExecution existing = merged.get(key);
                    if (existing != null) {
                        mergePluginExecution(element, existing, sourceDominant, context);
                    }
                    merged.put(key, element);
                }

                target.setExecutions(new ArrayList<>(merged.values()));
            }
        }
    }