Error: Expression dependency not found

Hi experts,

I'm using Bonita Community 7.2 and I'm having a problem with a database connector.

The conector has a sql code that have parameters:

begin
hr.abm.bonita_post_process(p_group_id => 1811,
p_new_status =>'${status}',
p_comments => '${approverComments}');
end;

When approverComments is null, then I get this exception, otherwise, it works fine:

GRAVE: THREAD_ID=598 | HOSTNAME=Arostegui | TENANT_ID=1 | The work [ExecuteConnectorOfActivity: flowNodeInstanceId = 420036, connectorDefinitionName = apexPostProcess] failed. The failure will be handled.
2016-06-16 16:31:57.089 +0200 org.bonitasoft.engine.execution.work.FailureHandlingBonitaWork org.bonitasoft.engine.log.technical.TechnicalLoggerSLF4JImpl log
GRAVE: THREAD_ID=598 | HOSTNAME=Arostegui | TENANT_ID=1 | org.bonitasoft.engine.expression.exception.SExpressionDependencyMissingException : "PROCESS_DEFINITION_ID=5628263928270836818 | PROCESS_NAME=AH Absences | PROCESS_VERSION=1.0 | PROCESS_INSTANCE_ID=20015 | ROOT_PROCESS_INSTANCE_ID=20015 | FLOW_NODE_DEFINITION_ID=5326936559902374252 | FLOW_NODE_INSTANCE_ID=420036 | FLOW_NODE_NAME=AH Manager Approve | CONNECTOR_IMPLEMENTATION_CLASS_NAME=apexPostProcess | CONNECTOR_INSTANCE_ID=220021 | Expression dependency not found: approverComments"
org.bonitasoft.engine.expression.exception.SExpressionDependencyMissingException: PROCESS_DEFINITION_ID=5628263928270836818 | PROCESS_NAME=AH Absences | PROCESS_VERSION=1.0 | PROCESS_INSTANCE_ID=20015 | ROOT_PROCESS_INSTANCE_ID=20015 | FLOW_NODE_DEFINITION_ID=5326936559902374252 | FLOW_NODE_INSTANCE_ID=420036 | FLOW_NODE_NAME=AH Manager Approve | CONNECTOR_IMPLEMENTATION_CLASS_NAME=apexPostProcess | CONNECTOR_INSTANCE_ID=220021 | Expression dependency not found: approverComments
at org.bonitasoft.engine.expression.impl.PatternExpressionExecutorStrategy.evaluate(PatternExpressionExecutorStrategy.java:45)
at org.bonitasoft.engine.expression.impl.PatternExpressionExecutorStrategy.evaluate(PatternExpressionExecutorStrategy.java:34)
at org.bonitasoft.engine.expression.impl.ExpressionServiceImpl.evaluate(ExpressionServiceImpl.java:86)
at org.bonitasoft.engine.core.expression.control.api.impl.ExpressionResolverServiceImpl.evaluateExpressionWithResolvedDependencies(ExpressionResolverServiceImpl.java:213)
at org.bonitasoft.engine.core.expression.control.api.impl.ExpressionResolverServiceImpl.evaluateExpressionsFlatten(ExpressionResolverServiceImpl.java:120)
at org.bonitasoft.engine.core.expression.control.api.impl.ExpressionResolverServiceImpl.evaluate(ExpressionResolverServiceImpl.java:83)
at org.bonitasoft.engine.core.connector.impl.ConnectorServiceImpl.evaluateInputParameters(ConnectorServiceImpl.java:294)
at org.bonitasoft.engine.connector.ConnectorServiceDecorator.evaluateInputParameters(ConnectorServiceDecorator.java:102)
at org.bonitasoft.engine.execution.work.ExecuteConnectorWork$EvaluateParameterAndGetConnectorInstance.call(ExecuteConnectorWork.java:223)
at org.bonitasoft.engine.execution.work.ExecuteConnectorWork$EvaluateParameterAndGetConnectorInstance.call(ExecuteConnectorWork.java:182)
at org.bonitasoft.engine.transaction.JTATransactionServiceImpl.executeInTransaction(JTATransactionServiceImpl.java:312)
at org.bonitasoft.engine.execution.work.ExecuteConnectorWork.work(ExecuteConnectorWork.java:134)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:42)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:42)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:42)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:42)
at org.bonitasoft.engine.execution.work.FailureHandlingBonitaWork.work(FailureHandlingBonitaWork.java:66)
at org.bonitasoft.engine.work.BonitaWork.run(BonitaWork.java:56)
at org.bonitasoft.engine.work.SequenceRunnableExecutor.innerRun(SequenceRunnableExecutor.java:47)
at org.bonitasoft.engine.work.BonitaRunnable.run(BonitaRunnable.java:35)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

Do you know how can I solve this? Some sort of nvl function?

Thanks,
Jose.