Issue 36: Introduce optional variables

README.md

@@ -21,13 +21,15 @@ Use the following expression in a ServiceTask to send all the process instance v
 ```
 ${camel.sendTo('<camel endpoint>')}
 ```
+Hint: You will also get variables which were set but contain a null value.
 
 Alternatively you can specify which process instance variables you want to send to Camel with:
 
 ```
 ${camel.sendTo('<camel endpoint>', '<comma-separated list of process variables>')}
 ```
-
+Hint: missing or null value variables will cause to throw an IllegalArgumentException. You can append a question mark to each name of a variable which is allowed to be missing or null (e.g. 'mayBeNullVar?,mustNotBeNullVar').
+
 Additionally you can specify a correlationKey to send to Camel. It can be used to correlate a response message. The route for the response must contain a parameter correlationKeyName with the name of the process variable which is used for correlation:
 
 ```

camunda-bpm-camel-common/src/main/java/org/camunda/bpm/camel/common/CamelServiceCommonImpl.java

@@ -8,7 +8,9 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedList;
 import java.util.Map;
+import java.util.Set;
 
 import org.apache.camel.CamelContext;
 import org.apache.camel.Exchange;
@@ -44,9 +46,15 @@ public Object sendTo(String endpointUri, String processVariables,
       String correlationId) {
     Collection<String> vars;
     if (processVariables == null) {
+      vars = new LinkedList<String>();
       ActivityExecution execution = Context.getBpmnExecutionContext()
           .getExecution();
-      vars = execution.getVariableNames();
+      final Set<String> variableNames = execution.getVariableNames();
+      if (variableNames != null) {
+        for (String variableName : variableNames) {
+          vars.add(variableName + "?");
+        }
+      }
     } else if ("".equals(processVariables)) {
       vars = Collections.emptyList();
     } else {
@@ -61,10 +69,15 @@ private Object sendToInternal(String endpointUri,
         .getBpmnExecutionContext().getExecution();
     Map<String, Object> variablesToSend = new HashMap<String, Object>();
     for (String var : variables) {
-      Object value = execution.getVariable(var);
-      if (value == null) {
-        throw new IllegalArgumentException("Process variable '" + var
-            + "' no found!");
+      Object value;
+      if (var.endsWith("?")) {
+        value = execution.getVariable(var.substring(0, var.length() - 1));
+      } else {
+        value = execution.getVariable(var);
+        if (value == null) {
+          throw new IllegalArgumentException("Process variable '" + var
+              + "' no found!");
+        }
       }
       variablesToSend.put(var, value);
     }