Please help me in handling java.lang.StringIndexOutOfBoundsException: String index out of range: -1 error

Hi all,

I am very new to cfscripts.

I am having below function  <cffunction name="newReplace" > and whenever I am calling this function I am getting java.lang.StringIndexOutOfBoundsException: String index out of range: -1 error.

I think I missed some validation to check the null but unable to identify.

<cffunction name="newReplace" returntype="string" description="Replace the original CF9 Replace() and ReplaceNoCase() which don't support some UTF-8 string">

  <cfargument name="stg" type="string">

  <cfargument name="origStg" >

  <cfargument name="rplStg" >

  <cfargument name="all" type="boolean" default=true>

  <cfargument name="caseSensitive" type="boolean" default=false>

  <cfset var result="">

  <cfscript>

  var oStringBuffer = createObject("java","java.lang.StringBuffer");

  var i = 0;

  var tmpStg = "";

  oStringBuffer = oStringBuffer.init(arguments.stg);

  while(i + origStg.length() <= oStringBuffer.length()) {

  tmStg = oStringBuffer.substring(i, i + origStg.length());

  if(tmStg.equalsIgnoreCase(origStg)) {

  oStringBuffer.replace(i, i + origStg.length(), rplStg);

  if(!all)

  break;

  else

  i += rplStg.length();

  }

  else

  i++;

  }

  result = oStringBuffer.toString();

  </cfscript>

  <cfreturn result/>

  </cffunction>

function call:

<cfset sndMsg = newReplace(sndMsg,"%EXPIRYDATE%",expiryDate,"ALL")>

error:

java.lang.StringIndexOutOfBoundsException: String index out of range: -1

at java.lang.String.substring(Unknown Source)

at coldfusion.runtime.StringFunc.Replace(StringFunc.java:390)

at coldfusion.runtime.CFPage.newReplace(CFPage.java:2633)