Support null cluster file

This is ok, it will get it from the environment variable if it is
null, but we can't set the environment variable to null.

Author: ScottDugas

yaml-tests/src/main/java/com/apple/foundationdb/relational/yamltests/YamlTestExtension.java

@@ -64,13 +64,14 @@ public class YamlTestExtension implements TestTemplateInvocationContextProvider,
     private List<YamlTestConfig> testConfigs;
     private List<YamlTestConfig> maintainConfigs;
     private List<ExternalServer> servers;
+    @Nullable
     private final String clusterFile;
 
     public YamlTestExtension() {
-        this.clusterFile = System.getenv("FDB_CLUSTER_FILE");
+        this.clusterFile = null; // it will get it from the environment
     }
 
-    public YamlTestExtension(final String clusterFile) {
+    public YamlTestExtension(@Nullable final String clusterFile) {
         this.clusterFile = clusterFile;
     }
 

yaml-tests/src/main/java/com/apple/foundationdb/relational/yamltests/server/ExternalServer.java

@@ -25,6 +25,7 @@
 import org.apache.logging.log4j.Logger;
 import org.junit.jupiter.api.Assertions;
 
+import javax.annotation.Nullable;
 import java.io.File;
 import java.io.IOException;
 import java.util.Arrays;
@@ -43,19 +44,22 @@ public class ExternalServer {
     public static final String EXTERNAL_SERVER_PROPERTY_NAME = "yaml_testing_external_server";
     private static final boolean SAVE_SERVER_OUTPUT = false;
 
+    @Nullable
     private final File serverJar;
     private final int grpcPort;
     private final int httpPort;
     private SemanticVersion version;
     private Process serverProcess;
-    private String clusterFile;
+    @Nullable
+    private final String clusterFile;
 
     /**
      * Create a new instance that will run a specific jar.
      *
      * @param serverJar the path to the jar to run
      */
-    public ExternalServer(File serverJar, final int grpcPort, final int httpPort, final String clusterFile) {
+    public ExternalServer(@Nullable File serverJar, final int grpcPort, final int httpPort,
+                          @Nullable final String clusterFile) {
         this.serverJar = serverJar;
         this.grpcPort = grpcPort;
         this.httpPort = httpPort;
@@ -123,7 +127,9 @@ public void start() throws Exception {
                                       ProcessBuilder.Redirect.DISCARD;
         processBuilder.redirectOutput(out);
         processBuilder.redirectError(err);
-        processBuilder.environment().put("FDB_CLUSTER_FILE", clusterFile);
+        if (clusterFile != null) {
+            processBuilder.environment().put("FDB_CLUSTER_FILE", clusterFile);
+        }
 
         if (!startServer(processBuilder)) {
             Assertions.fail("Failed to start the external server");