I think I have a solution. Well, it worked for me.
In the ezfind extension, there is a lack in the setting file "settings/ezfind.ini".
Here is the modified category of my file :
[SolrFieldMapSettings]
# List of custom datatype mapping. eZ Publish datatype string is used
# as key, and the value if the name of the class to use.
#
# Example:
# CustomMap[eztext]=ezfSolrDocumentFieldText
CustomMap[ezobjectrelation]=ezfSolrDocumentFieldObjectRelation
CustomMap[ezobjectrelationlist]=ezfSolrDocumentFieldObjectRelation
CustomMap[ezxmltext]=ezfSolrDocumentFieldXML
CustomMap[ezmatrix]=ezfSolrDocumentFieldXML
# Datatype to field type map.
#
# Example:
DatatypeMap[ezstring]=string
DatatypeMap[eztext]=text
DatatypeMap[ezboolean]=boolean
DatatypeMap[ezdate]=date
DatatypeMap[ezdatetime]=date
DatatypeMap[ezfloat]=sfloat
DatatypeMap[ezinteger]=sint
DatatypeMap[ezprice]=sfloat
DatatypeMap[eztime]=date
# Default field type
Default=text
The only difference with the initial file is the line :