How do I overcome "object literals cannot contain duplicate keys in ES5 strict mode" error with Maven minify plugin?

I'm using the Maven minify plugin with Maven 3.5. I have the below configuration ...

                <plugin>
                    <groupId>com.samaxes.maven</groupId>
                    <artifactId>minify-maven-plugin</artifactId>
                    <version>1.7.6</version>
                    <executions>
                        <execution>
                            <id>default-minify</id>
                            <phase>verify</phase>
                            <configuration>
                                <cssSourceIncludes>
                                    <cssSourceInclude>**/*.css</cssSourceInclude>
                                </cssSourceIncludes>
                                <cssTargetDir>../${project.artifactId}/css</cssTargetDir>
                                <jsSourceExcludes>
                                    <jsSourceExclude>lib/pdf.js</jsSourceExclude>
                                    <jsSourceExclude>lib/pdf.worker.js</jsSourceExclude>
                                    <jsSourceExclude>ckeditor_4.2/**</jsSourceExclude>
                                    <jsSourceExclude>geogebra/**</jsSourceExclude>
                                    <jsSourceExclude>contextMenu/**</jsSourceExclude>
                                    <jsSourceExclude>wPaint/**</jsSourceExclude>
                                </jsSourceExcludes>
                                <jsSourceIncludes>
                                    <jsSourceInclude>**/*.js</jsSourceInclude>
                                </jsSourceIncludes>
                                <jsTargetDir>../${project.artifactId}/js</jsTargetDir>
                                <jsEngine>CLOSURE</jsEngine>
                                <webappTargetDir>${project.build.outputDirectory}</webappTargetDir>
                                <skipMerge>true</skipMerge>
                                <nosuffix>true</nosuffix>
                            </configuration>
                            <goals>
                                <goal>minify</goal>
                            </goals>
                        </execution>
                    </executions>
                </plugin>

However, I'm getting this error on the below file ...

SEVERE: panel.js:845: ERROR -  with         

    SIDE_PANEL_BEGIN_CLOSE_EVENT:SIDE_PANEL_BEGIN_CLOSE_EVENT,
            ^

    Nov 27, 2018 2:57:06 PM com.google.javascript.jscomp.LoggerErrorManager printSummary
    WARNING: 1 error(s), 0 warning(s)

Everything works in my application fine with my uncompressed file so I'm thinking I just made a mistake with my configuration but I can't see what. How can I correct the configuration so that the optimization occurs without the error without affecting the underlying functionality of the code?

Solution

While Google's Closure Compiler (which is used under the hood by the minify plugin to optimize the source code) by default expects ECMAScript 6 as input language it seems to run additional diagnostic checks which do not take the language level into account.

These diagnostic checks include one for ECMAScript 5 strict mode compliance which forbids duplicate keys in objects.

As described in this answer by Sebstian Häger you can turn this diagnostic check of in the minify configuration by adding

<closureWarningLevels>
    <es5Strict>OFF</es5Script>
</closureWarningLevels>