Below is the WorkItem Definition which I used to create Email and Log Nodes as you Suggested Tihomir. I did not give value to icon.
import org.drools.process.core.datatype.impl.type.StringDataType;
[
[
"name" : "Email",
"parameters" : [
"From" : new StringDataType(),
"To" : new StringDataType(),
"Subject" : new StringDataType(),
"Body" : new StringDataType()
],
"displayName" : "Email",
"icon" : ""
],
[
"name" : "Log",
"parameters" : [
"Message" : new StringDataType()
],
"displayName" : "Log",
"icon" : ""
]
]