Do not get UPPERCASE env vars

src/main/java/org/codehaus/mojo/exec/ExecMojo.java

@@ -478,7 +478,13 @@ public void execute() throws MojoExecutionException {
     private Map<String, String> handleSystemEnvVariables() throws MojoExecutionException {
 
         Map<String, String> enviro = new HashMap<>();
-        Properties systemEnvVars = CommandLineUtils.getSystemEnvVars();
+
+        // Avoid creating env vars that differ only in case on Windows.
+        // https://github.com/mojohaus/exec-maven-plugin/issues/328
+        // It is not enough to avoid duplicates; we must preserve the case found in the "natural" environment.
+        // https://developercommunity.visualstudio.com/t/Build-Error:-MSB6001-in-Maven-Build/10527486?sort=newest
+        Properties systemEnvVars = CommandLineUtils.getSystemEnvVars(true);
+
         for (Map.Entry<?, ?> entry : systemEnvVars.entrySet()) {
             enviro.put((String) entry.getKey(), (String) entry.getValue());
         }