Random concurrent modification exception when receiving message from http channel

**2.7.4**

**Message always received from http channel**

**Concurrent Modification Exception is randomly reproduced**

Caused by: java.util.ConcurrentModificationException
at java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:719)
at java.util.LinkedHashMap$LinkedEntryIterator.next(LinkedHashMap.java:752)
at java.util.LinkedHashMap$LinkedEntryIterator.next(LinkedHashMap.java:750)
at java.util.AbstractMap.toString(AbstractMap.java:554)
at java.util.Collections$UnmodifiableMap.toString(Collections.java:1495)
at java.lang.String.valueOf(String.java:2994)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at com.consol.citrus.message.DefaultMessage.toString(DefaultMessage.java:104)
at java.lang.String.valueOf(String.java:2994)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at org.springframework.messaging.support.GenericMessage.toString(GenericMessage.java:111)
at java.lang.String.valueOf(String.java:2994)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:432)

Start with DefaultMessage.java at DefaultMessage.toString(), then trace the message through GenericMessage.toString() and AbstractMessageChannel.send() while reproducing receipt from the HTTP channel. The issue is resolved when concurrent message receipt no longer produces the reported ConcurrentModificationException.

Written by the indexing model from the issue text.