NullPointer when I try to specify a schematron via command-line without a schema

[jordanpadams]

🐛 Describe the bug

When i specify a schematron + schema via command-line, it works as expected. But when I only specify a schematron, it throws a nullpointerexception

📜 To Reproduce

validate-2.1.0-SNAPSHOT/bin/validate -t ccb-327_NoSchematron.xml --skip-content-validation \
          -S ./src/main/resources/schema/1B00/PDS4_PDS_1B00.sch

🕵️ Expected behavior

Executes same as if I specified schematron + schema via command-line, but uses the schema specified in the label.

📚 Version of Software Used

Version 2.1.0-SNAPSHOT Release Date: 2021-04-23 09:28:05

🩺 Test Data / Additional context

ccb-327_NoSchematron.xml.txt

🏞Screenshots

PDS Validate Tool Report

Configuration:
   Version                       2.1.0-SNAPSHOT
   Date                          2021-04-23T18:17:59Z

Parameters:
   Targets                       [file:/Users/jpadams/Documents/proj/pds/pdsen/workspace/validate/ccb-327_NoSchematron.xml]
   User Specified Schematrons    [file:/Users/jpadams/Documents/proj/pds/pdsen/workspace/validate/src/main/resources/schema/1B00/PDS4_PDS_1B00.sch]
   Severity Level                WARNING
   Recurse Directories           true
   File Filters Used             [*.xml, *.XML]
   Data Content Validation       off
   Product Level Validation      on
   Max Errors                    100000
   Registered Contexts File      /Users/jpadams/Documents/proj/pds/pdsen/workspace/validate/validate-2.1.0-SNAPSHOT/resources/registered_context_products.json



Product Level Validation Results

  FAIL: file:/Users/jpadams/Documents/proj/pds/pdsen/workspace/validate/ccb-327_NoSchematron.xml
      ERROR  [error.validation.internal_error]   Error executing validationTask: java.lang.NullPointerException
        1 product validation(s) completed

🖥 System Info

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

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** :unicorn: Applicable requirements**