Filters out null matrix parameters

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/annotation/MatrixVariableParameterProcessor.java

@@ -75,9 +75,8 @@ public class MatrixVariableParameterProcessor implements AnnotatedParameterProce
 	private String expandMap(Object object) {
 		Map<String, Object> paramMap = (Map) object;
 
-		return paramMap.keySet().stream()
-				.map(key -> ";" + key + "=" + paramMap.get(key).toString())
-				.collect(Collectors.joining());
+		return paramMap.keySet().stream().filter(key -> paramMap.get(key) != null)
+				.map(key -> ";" + key + "=" + paramMap.get(key).toString()).collect(Collectors.joining());
 	}
 
 }