Pass an optional property from main oozie workflow to subworkflow - hadoop

Question

I have an HDFS_file_path or property that needs to be passed from workflow-1 to common_subworkflow.
I also have workflow-2 which doesn't have that property or HDFS_file_path. But workflow-2 calls common_subworkflow.
In common_subworkflow I am fetching the property value with ${HDFS_file_path}.
It works fine when workflow-1 calls common_subworkflow but fails when workflow-2 calls common_subworkflow since HDFS_file_path doesn't exist in workflow-2.
Is there any way to
read the dynamic property if present, or
set some default value(null or empty) if variable not present

Answer 1

<workflow-app name='hello-wf' xmlns="uri:oozie:workflow:0.4">
<parameters>
<property>
<name>inputDir</name>
</property>
<property>
<name>outputDir</name>
<value>out-dir</value>
</property>
</parameters>
...
<action name='firstjob'>
<map-reduce>
<job-tracker>${jobTracker}</job-tracker>
<name-node>${nameNode}</name-node>
<configuration>
<property>
<name>mapred.mapper.class</name>
<value>com.foo.FirstMapper</value>
</property>
<property>
<name>mapred.reducer.class</name>
<value>com.foo.FirstReducer</value>
</property>
<property>
<name>mapred.input.dir</name>
<value>${inputDir}</value>
</property>
<property>
<name>mapred.output.dir</name>
<value>${outputDir}</value>
</property>
</configuration>
</map-reduce>
<ok to='secondjob'/>
<error to='killcleanup'/>
</action>
...
</workflow-app>
In the above example, if inputDir is not specified, Oozie will print an error message instead of submitting the job. If =outputDir= is not specified, Oozie will use the default value, out-dir .
Taken from https://oozie.apache.org/docs/3.3.1/WorkflowFunctionalSpec.html#a4.1_Workflow_Job_Properties_or_Parameters