Cannot create JDBC driver of class '' for connect URL 'null'

If you get this Exception while using Tomcat 5.5.9 or 5.5.*

Caused by: org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null' at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:780) at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:540) at com.vsnl.pcr.dao.DataAccessObject.getConnection(DataAccessObject.java:119) ... 29 more

Possible Solution:
Check the database lookup entry in either context.xml or server.xml
In Tomcat 5.5.9 there are no <ResouceParams> tag and the parameters are passed alongiwth the resource tag.

e.g Resource Entry in Tomcat 5.5.9

<resource name="jdbc/XYZ"
    auth="Container"
    scope="Shareable"
    type="javax.sql.DataSource"
    driverclassname="oracle.jdbc.driver.OracleDriver"
    url="jdbc:oracle:thin:@xxx.xxx.xxx.xxx:1521:XYZ"
    username="xyz"
    password="xyz"
    maxactive="10"
    maxidle="100"
    maxwait="3000">
</resource>

In Tomcat 5.0.28

<resource name="jdbc/XYZ" scope="Shareable" type="javax.sql.DataSource">
<resourceparams name="jdbc/XYZ">
<parameter>
  <name>factory</name>
  <value>
      org.apache.commons.dbcp.BasicDataSourceFactory
  </value>
</parameter>
<!-- DBCP database connection settings  -->
<parameter>
  <name>url</name>
   <value>jdbc:oracle:thin:@xxx.xxx.xxx.xxx:1521:XYZ</value>
</parameter>
<parameter>
  <name>driverClassName</name>
  <value>oracle.jdbc.driver.OracleDriver</value>
</parameter>
<parameter>
  <name>username</name>
  <value>xyz</value>
</parameter>
<parameter>
  <name>password</name>
  <value>xyz</value>
</parameter>
<parameter>
  <name>maxWait</name>
  <value>3000</value>
</parameter>
<parameter>
  <name>maxIdle</name>
  <value>100</value>
</parameter>
<parameter>
  <name>maxActive</name>
  <value>10</value>
</parameter>

</resourceparams>
</resource> 

One Last Point: Dont forget to put your classes12.jar/ojdbc14.jar file in /commons/lib folder.

Two useful links which help me discover this.. :-) (after I had already wasted a lot of time)
1. Java Forums
2. Tomcat Docs