错误代码：
0 ERROR [main] freemarker.runtime --Error executing FreeMarker template 03 七月 14:25:32,730
FreeMarker template error:
The following has evaluated to null or missing:
==> json [in template "template.ftl" at line 56, column 49]
Tip: If the failing expression is known to be legally null/missing, either specify a default value with myOptionalVar!myDefault, or use when-presentwhen-missing#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthessis: (myOptionVar.foo)!myDefault, (myOptionVar.foo)??
The failing instruction (FTL stack trace):
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==> ${json[0]} [in template "template.ftl" at line 56, column 47]
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Java stack trace (for programmers):
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freemarker.core.InvalidReferenceException: [... Exception message was already p
