params - parameters passed containig the context information.
returnType - data type of the returned value. This can be passed as null.
If no return type is specified, an Iterator of Map will be returned.
Object of the type defined by the returnType parameter.
If the type is available, an instance of that object is created. If no
type is specified an Iterator of Map objects
for the result will be created.
If no data found it can return null. The Map
contains the value of attributes as defined in the data structure.
For complex data, Maps can contain other
Maps as well.