Character reference “ ” is an invalid XML character Mirth Error

I was bringing a text document into an HL7 messages today in Mirth when I found I got the following error every time for a particular document.

ER7Serializer error
ERROR MESSAGE: Error converting XML to ER7
org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 47427; Character reference "&#12" is an invalid XML character.
    at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
    at org.apache.xerces.util.ErrorHandlerWrapper.fatalError(Unknown Source)
    at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
    at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
    at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
    at org.apache.xerces.impl.XMLScanner.reportFatalError(Unknown Source)
    at org.apache.xerces.impl.XMLScanner.scanCharReferenceValue(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanCharReference(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
    at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
    at com.mirth.connect.plugins.datatypes.hl7v2.ER7Serializer.fromXML(ER7Serializer.java:277)
    at com.mirth.connect.donkey.server.channel.FilterTransformerExecutor.processConnectorMessage(FilterTransformerExecutor.java:123)
    at com.mirth.connect.donkey.server.channel.DestinationConnector.transform(DestinationConnector.java:320)
    at com.mirth.connect.donkey.server.channel.DestinationChain.call(DestinationChain.java:151)
    at com.mirth.connect.donkey.server.channel.Channel.process(Channel.java:1653)
    at com.mirth.connect.donkey.server.channel.Channel.dispatchRawMessage(Channel.java:1156)
    at com.mirth.connect.donkey.server.channel.SourceConnector.dispatchRawMessage(SourceConnector.java:192)
    at com.mirth.connect.donkey.server.channel.SourceConnector.dispatchRawMessage(SourceConnector.java:170)
    at com.mirth.connect.connectors.ws.WebServiceReceiver.processData(WebServiceReceiver.java:238)
    at com.mirth.connect.connectors.ws.WebServiceReceiver.processData(WebServiceReceiver.java:207)
    at com.mirth.connect.connectors.ws.DefaultAcceptMessage.acceptMessage(DefaultAcceptMessage.java:24)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.Trampoline.invoke(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.sun.xml.internal.ws.api.server.MethodUtil.invoke(Unknown Source)
    at com.sun.xml.internal.ws.api.server.InstanceResolver$1.invoke(Unknown Source)
    at com.sun.xml.internal.ws.server.InvokerTube$2.invoke(Unknown Source)
    at com.sun.xml.internal.ws.server.sei.SEIInvokerTube.processRequest(Unknown Source)
    at com.sun.xml.internal.ws.api.pipe.Fiber.__doRun(Unknown Source)
    at com.sun.xml.internal.ws.api.pipe.Fiber._doRun(Unknown Source)
    at com.sun.xml.internal.ws.api.pipe.Fiber.doRun(Unknown Source)
    at com.sun.xml.internal.ws.api.pipe.Fiber.runSync(Unknown Source)
    at com.sun.xml.internal.ws.server.WSEndpointImpl$2.process(Unknown Source)
    at com.sun.xml.internal.ws.transport.http.HttpAdapter$HttpToolkit.handle(Unknown Source)
    at com.sun.xml.internal.ws.transport.http.HttpAdapter.handle(Unknown Source)
    at com.sun.xml.internal.ws.transport.http.server.WSHttpHandler.handleExchange(Unknown Source)
    at com.sun.xml.internal.ws.transport.http.server.WSHttpHandler.handle(Unknown Source)
    at com.sun.net.httpserver.Filter$Chain.doFilter(Unknown Source)
    at sun.net.httpserver.AuthFilter.doFilter(Unknown Source)
    at com.sun.net.httpserver.Filter$Chain.doFilter(Unknown Source)
    at sun.net.httpserver.ServerImpl$Exchange$LinkHandler.handle(Unknown Source)
    at com.sun.net.httpserver.Filter$Chain.doFilter(Unknown Source)
    at sun.net.httpserver.ServerImpl$Exchange.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

So, this looks like it’s caused by a funny character – the "&#12" or Form Feed.  I found the transformer that was bringing in the value and tried at first to try/catch it out, but quickly found that my JavaScript code wasn’t the problem, it was actually internal Mirth code getting all tripped up by the character.

That means that the only way to fix it now is to remove the character, but how?  I had actually written out the value to the logging window, where it was visible as a funny square box.  Very handy this as I was actually able to copy the value, and then do a string comparison to filter it out.