fix<mapper> null pointer in request mappers

Signed-off-by: Shijie Sheng <liouvetren@gmail.com>

Author: shijiesheng

src/main/java/com/uber/cadence/internal/compatibility/proto/mappers/DecisionMapper.java

@@ -157,7 +157,7 @@ static Decision decision(com.uber.cadence.Decision d) {
               d.getRequestCancelExternalWorkflowExecutionDecisionAttributes();
           RequestCancelExternalWorkflowExecutionDecisionAttributes.Builder builder =
               RequestCancelExternalWorkflowExecutionDecisionAttributes.newBuilder()
-                  .setDomain(attr.getDomain())
+                  .setDomain(attr.getDomain() != null ? attr.getDomain() : "")
                   .setWorkflowExecution(workflowRunPair(attr.getWorkflowId(), attr.getRunId()))
                   .setChildWorkflowOnly(attr.isChildWorkflowOnly());
           if (attr.getControl() != null) {

src/main/java/com/uber/cadence/internal/compatibility/proto/mappers/TypeMapper.java

@@ -128,7 +128,7 @@ static WorkflowExecution workflowRunPair(String workflowId, String runId) {
     if (Strings.isNullOrEmpty(workflowId) && Strings.isNullOrEmpty(runId)) {
       return WorkflowExecution.newBuilder().build();
     }
-    return WorkflowExecution.newBuilder().setWorkflowId(workflowId).setRunId(runId).build();
+    return WorkflowExecution.newBuilder().setWorkflowId(workflowId).setRunId(runId != null ? runId : "").build();
   }
 
   static ActivityType activityType(com.uber.cadence.ActivityType t) {
@@ -275,7 +275,7 @@ static WorkflowExecutionFilter workflowExecutionFilter(
     }
     return WorkflowExecutionFilter.newBuilder()
         .setWorkflowId(t.getWorkflowId())
-        .setRunId(t.getRunId())
+        .setRunId(t.getRunId() != null ? t.getRunId() : "")
         .build();
   }