django_elasticsearch_dsl -RequestError(400, 'search_phase_execution_exception', 'failed to create query: For input string: )

Question

I am trying to search with Elasticsearch using django_elasticsearch_dsl and 'django_elasticsearch_dsl_drf',, but I get RequestError(400, 'search_phase_execution_exception', 'failed to create query: For input string: "MM"'). I am able to search if my input is an integer or a float , but I am not able to search for string. Here is my document.py file:-

from django_elasticsearch_dsl import (
    Document ,
    fields,
    Index,
)
#from .models import ElasticDemo
from .models import Course
#PUBLISHER_INDEX = Index('elastic_demo')
PUBLISHER_INDEX = Index('courses') #Name of the database that we are making
PUBLISHER_INDEX.settings(
    number_of_shards=1,
    number_of_replicas=1
)


@PUBLISHER_INDEX.doc_type
class CourseDocument(Document):
    id = fields.IntegerField(attr='id')
    #fielddata=True
    
    course_index = fields.IntegerField(
        fields={
            'raw': fields.IntegerField(analyzer='keyword'),
        }
    )

    

    Code = fields.TextField(
        fields={
            'raw': fields.TextField(analyzer='keyword'),
        }
    )


    Title = fields.TextField(
         fields={
            'raw': fields.TextField(analyzer='keyword'),
        }
    )

    TotalCredits = fields.FloatField(
         fields={
            'raw': fields.TextField(analyzer='keyword'),
        }
    )



    Description = fields.TextField(
         fields={
            'raw': fields.TextField(analyzer='keyword'),
        }
    )

    department = fields.TextField(
         fields={
            'raw': fields.TextField(analyzer='keyword'),
        }
    )


    class Django(object):
        model = Course

Here is my views.py

class CourseDocumentView(DocumentViewSet):
   
    document = CourseDocument 
    serializer_class = CourseSerializer 
    lookup_field = 'id'
    filter_backends = [
        FilteringFilterBackend,
        OrderingFilterBackend,
        CompoundSearchFilterBackend,
        #DefaultOrderingFilterBackend,
        SearchFilterBackend,
    ]
    search_fields = (
        'Code',
        'Title',
        'TotalCredits',
        'Description',
        'department',
    )
    multi_match_search_fields = (
        'Code',
        'Title',
        'TotalCredits',
        'Description',
        'department',
    )
    filter_fields = {
        'Code' :  'Code',
        'Title' : 'Title',
        'TotalCredits' : 'TotalCredits',
        'Description': 'Description',
        'department': 'department' ,
    }
    ordering_fields = {
        'Code':None,
        'TotalCredits':None,
        'Title':None,
    }
    ordering = ( 'id'  , )

    pagination_class = QueryFriendlyPageNumberPagination

And here is my serializer:-

import json
from .models import Course
from rest_framework import serializers
from django_elasticsearch_dsl_drf.serializers import DocumentSerializer
from .documents import *


class CourseSerializer(DocumentSerializer):

    

    class Meta(object):
        """Meta options"""
        model = Course
        document = CourseDocument
        fields = (
            'course_index',
            'Code',
            'Title',
            'TotalCredits',
            'Description',
            'department',
        )
        def get_location(self, obj):
            """Represent location value."""
            try:
                return obj.location.to_dict()
            except:
                return {}

I am new to elasticsearch. Any help will be highly appreciated !