A clean checkout of https://github.com/apache/poi does not compile and aborts with a build error. This prevents contributions via github pull requests.

See console below console output from my machine:

```
xiaolong:poi-upstream axel$ git remote -v
origin  https://github.com/apache/poi (fetch)
origin  https://github.com/apache/poi (push)
xiaolong:poi-upstream axel$ git pull  
Already up to date.
xiaolong:poi-upstream axel$ git status
On branch trunk
Your branch is up to date with 'origin/trunk'.

nothing to commit, working tree clean
xiaolong:poi-upstream axel$ ant jar
Buildfile: /Users/axel/Development/FOSS/poi-upstream/build.xml
[propertyreset] Warning: Nashorn engine is planned to be removed from a future JDK release
[propertyreset] Warning: Nashorn engine is planned to be removed from a future JDK release

check-jars:

fetch-jars:

check-ooxml-jars:

fetch-ooxml-jars:

init:
     [echo] Using Ant: Apache Ant(TM) version 1.10.7 compiled on September 1 2019 from /Users/axel/bin/apache-ant-1.10.7, Ant detected Java 13 (may be different than actual Java sometimes...)
     [echo] Using Java: 13/13+33/13+33/OpenJDK 64-Bit Server VM from Azul Systems, Inc. on Mac OS X: 10.14.6
[release_tag] Warning: Nashorn engine is planned to be removed from a future JDK release

compile-main:

check-ooxml-xsds:

fetch-ooxml-xsds:

generate-geometry:

compile-scratchpad:
    [javac] Compiling 204 source files to /Users/axel/Development/FOSS/poi-upstream/build/scratchpad-test-classes
    [javac] warning: [options] bootstrap class path not set in conjunction with -source 8
    [javac] /Users/axel/Development/FOSS/poi-upstream/src/scratchpad/testcases/org/apache/poi/hwpf/usermodel/TestBugs.java:49: error: package org.apache.poi.ooxml.util does not exist
    [javac] import org.apache.poi.ooxml.util.DocumentHelper;
    [javac]                                 ^
    [javac] 1 error
    [javac] 1 warning

BUILD FAILED
/Users/axel/Development/FOSS/poi-upstream/build.xml:1130: Compile failed; see the compiler error output for details.

Total time: 2 seconds
```

----------

It's the same error that shows in the CI build for my [pull request](https://github.com/apache/poi/pull/160) [log](https://builds.apache.org/view/P/view/POI/job/POI-DSL-Github-PullRequests/30/console):


```
compile-scratchpad:
    [javac] Compiling 510 source files to /home/jenkins/jenkins-slave/workspace/POI-DSL-Github-PullRequests/build/scratchpad-classes
    [javac] Note: Some input files use or override a deprecated API.
    [javac] Note: Recompile with -Xlint:deprecation for details.
    [javac] Note: Some input files use unchecked or unsafe operations.
    [javac] Note: Recompile with -Xlint:unchecked for details.
    [javac] Compiling 204 source files to /home/jenkins/jenkins-slave/workspace/POI-DSL-Github-PullRequests/build/scratchpad-test-classes
    [javac] /home/jenkins/jenkins-slave/workspace/POI-DSL-Github-PullRequests/src/scratchpad/testcases/org/apache/poi/hwpf/usermodel/TestBugs.java:49: error: package org.apache.poi.ooxml.util does not exist
    [javac] import org.apache.poi.ooxml.util.DocumentHelper;
    [javac]                                 ^
    [javac] 1 error

BUILD FAILED
/home/jenkins/jenkins-slave/workspace/POI-DSL-Github-PullRequests/build.xml:1130: Compile failed; see the compiler error output for details.

Total time: 1 minute 1 second
Build step 'Invoke Ant' marked build as failure
Skipping publisher since build result is FAILURE
Archiving artifacts
[Fast Archiver] Compressed 35.68 MB of artifacts by 99.8% relative to #29
Skipping publisher since build result is FAILURE
Recording test results
ERROR: Step ?Publish JUnit test result report? failed: No test report files were found. Configuration error?
Sending e-mails to: dev@poi.apache.org
Finished: FAILURE
```