Conversion failed exception from String to bson ObjectId on Mongo calls

Hi,
We are getting following error logged in Dynatrace on all Mongo calls even though app functions normally and we are also unable to see the exception when debugging through IDE:
Exception:
org.springframework.core.convert.ConversionFailedException
Message:
Failed to convert from type [java.lang.String] to type [org.bson.types.ObjectId] for value ''; nested exception is java.lang.IllegalArgumentException: invalid hexadecimal representation of an ObjectId: []
Stacktrace:
org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:47)
org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:191)
org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:174)
org.springframework.data.mongodb.core.convert.MongoConverter.convertId(MongoConverter.java:146)
org.springframework.data.mongodb.core.convert.QueryMapper.convertId(QueryMapper.java:636)
org.springframework.data.mongodb.core.convert.QueryMapper.getMappedValue(QueryMapper.java:384)
org.springframework.data.mongodb.core.convert.QueryMapper.getMappedObjectForField(QueryMapper.java:243)
org.springframework.data.mongodb.core.convert.QueryMapper.getMappedObject(QueryMapper.java:152)
org.springframework.data.mongodb.core.convert.QueryMapper.getMappedKeyword(QueryMapper.java:285)
org.springframework.data.mongodb.core.convert.QueryMapper.getMappedObject(QueryMapper.java:124)
org.springframework.data.mongodb.core.MongoTemplate.doFindOne(MongoTemplate.java:2473)
org.springframework.data.mongodb.core.MongoTemplate.findOne(MongoTemplate.java:820)
org.springframework.data.mongodb.core.MongoTemplate.findOne(MongoTemplate.java:807)
org.springframework.data.mongodb.core.MongoTemplate$$FastClassBySpringCGLIB$$5a5a6b8.invoke()
org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:769)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689)
com.company.config.MongoTemplateWithMetrics$$EnhancerBySpringCGLIB$$.findOne
com.company.dao.connect.AppointmentDAOConnect.findByParameterAppointment(AppointmentDAOConnect.java:689)
com.company.dao.connect.AppointmentDAOConnect$$FastClassBySpringCGLIB$$40444430.invoke()
org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:769)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689)
com.company.dao.connect.AppointmentDAOConnect$$EnhancerBySpringCGLIB$$.findByParameterAppointment

How can I go about debugging the issue?

Start by tracing MongoConverter.convertId and QueryMapper from the reported MongoTemplate.findOne call at AppointmentDAOConnect.java:689. Determine which query value is the invalid ObjectId string and whether it can be reproduced from the reported call; done means identifying the source of the value and a concrete corrective action.