fix: Adds an empty list to nonFilteredFileExtensions

without this change an NPE is being thrown from Maven Resources Filtering
with this change since the list is empty an NPE is no longer thrown

fixes #2361

Author: marcingrzejszczak

spring-cloud-contract-tools/spring-cloud-contract-maven-plugin/src/main/java/org/springframework/cloud/contract/maven/verifier/CopyContracts.java

@@ -82,7 +82,8 @@ public void copy(File contractsDirectory, File outputDirectory) throws MojoExecu
 		execution.setOverwrite(true);
 		execution.setIncludeEmptyDirs(false);
 		execution.setFilterFilenames(false);
-		execution.setFilters(Collections.emptyList());
+		execution.setFilters(Collections.<String>emptyList());
+		execution.setNonFilteredFileExtensions(Collections.<String>emptyList());
 		try {
 			this.mavenResourcesFiltering.filterResources(execution);
 		}