JsonMappingException when trying to transform a stubMapping to use regex urlPattern instead of standard url using Wiremock Java Library

Question

I'm trying to transform a stubMapping to detect the request using a regex, instead of using simple string equality. But When I do this, a NPE is thrown when the Json conversion is processed. When I debug the list of stubMappings which is converted when the NPE appears, the NPE is thrown when I try to get the element in the list which contains the stubMapping with the regex urlPattern, yet my transformer returns a stubmapping which is not null.

Here is the Exception:

Exception in thread "Timer-8" com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.google.common.collect.Lists$TransformingRandomAccessList[2])
    at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:397)
    at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:368)
    at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:338)
    at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:123)
    at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:79)
    at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:18)
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319)
    at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1516)
    at com.fasterxml.jackson.databind.ObjectWriter._writeValueAndClose(ObjectWriter.java:1217)
    at com.fasterxml.jackson.databind.ObjectWriter.writeValueAsString(ObjectWriter.java:1086)
    at com.github.tomakehurst.wiremock.common.Json.write(Json.java:88)
    at com.github.tomakehurst.wiremock.common.Json.write(Json.java:74)
    at com.github.tomakehurst.wiremock.recording.Recorder.stopRecording(Recorder.java:92)
    at com.github.tomakehurst.wiremock.core.WireMockApp.stopRecording(WireMockApp.java:486)
    at com.github.tomakehurst.wiremock.WireMockServer.stopRecording(WireMockServer.java:470)

And what I'm doing in my stub mapping transformer class:

@Override
public StubMapping transform(StubMapping stubMapping, FileSource fileSource, Parameters parameters) {
    RequestPattern originalRequest = stubMapping.getRequest();

    String urlPattern = originalRequest.getUrl();
    urlPattern = urlPattern.replaceAll("ownerName=(.*)&", Matcher.quoteReplacement("ownerName=(.*)&"));

    RequestPattern request = new RequestPattern(
                originalRequest.getScheme(),
                originalRequest.getHost(),
                originalRequest.getPort(),
                WireMock.urlMatching(urlPattern),
                originalRequest.getMethod(),
                originalRequest.getHeaders(),
                originalRequest.getQueryParameters(),
                originalRequest.getCookies(),
                originalRequest.getBasicAuthCredentials(),
                originalRequest.getBodyPatterns(),
                originalRequest.getCustomMatcher(),
                originalRequest.hasInlineCustomMatcher() ? originalRequest.getMatcher() : null,
                originalRequest.getMultipartPatterns()
        );

    stubMapping.setRequest(request);

    return stubMapping;
}

Can someone help me to solve this? Am I doing something wrong ? I didn't find out how to do it with the RequestPatternBuilder, so I did it directly with the RequestPattern constructor.

And the problem appears only when I use WireMock.urlMatching(urlPattern) for the url. When I replace it by WireMock.urlEqualTo(urlPattern) in my code, the NPE is not thrown anymore.

Thanks in advance.