title: Keycloak fails because it can't find my theme or default theme with NullPointer Exception
body: <p>I had a working local keycloak image when I had to nuke all my docker images for another issue. I then brought up my keycloak image again with </p>
  
  <pre><code>version: '3.6'
  
  volumes:
    keycloak_postgres_data: {}
  
  services:
    postgres-keycloak:
        image: postgres:10-alpine
        container_name: postgres
        volumes:
          - keycloak_postgres_data:/var/lib/postgresql/data
        environment:
          POSTGRES_DB: keycloak
          POSTGRES_USER: keycloak
          POSTGRES_PASSWORD: password
  
    keycloak:
        image: jboss/keycloak:4.1.0.Final
        environment:
          DB_VENDOR: POSTGRES
          DB_ADDR: postgres
          DB_DATABASE: keycloak
          DB_USER: keycloak
          DB_PASSWORD: password
          KEYCLOAK_USER: admin
          KEYCLOAK_PASSWORD: testing
        ports:
          - 8088:8080
        volumes:
          - ./themes/puretalent:/opt/jboss/keycloak/themes/puretalent
          - ./themes/fifteenrock:/opt/jboss/keycloak/themes/fifteenrock
        depends_on:
          - postgres-keycloak
  
  </code></pre>
  
  <p>The themes mentioned in the volume are present in the same folder and are also in the container when I bring it up. In the Realm Settings, I have tried, setting the theme to my specific theme or to the default theme but I get the same error below. I’ve elided it to the relevant error messages. I have also disable cache in the standalone.xml and restarted the container.</p>
  
  <p>However, I'm getting a NullPointer exception. </p>
  
  <pre><code>keycloak_1 |
  keycloak_1 | 01:18:58,781 WARN [org.keycloak.events] (default task-1) type=LOGIN_ERROR, realmId=master, clientId=odin, userId=null, ipAddress=172.20.0.1, error=invalid_user_credentials, auth_method=openid-connect, auth_type=code, response_type=code, redirect_uri=http://localhost:8082/odin/oidc_callback, code_id=9646b75e-273d-473e-a999-643d01d4cc36, response_mode=query
  keycloak_1 | 01:18:58,793 ERROR [org.keycloak.services.error.KeycloakErrorHandler] (default task-1) Uncaught server error: java.lang.NullPointerException
  keycloak_1 | at org.keycloak.theme.ExtendingThemeManager.loadTheme(ExtendingThemeManager.java:117)
  keycloak_1 | at org.keycloak.theme.ExtendingThemeManager.getTheme(ExtendingThemeManager.java:108)
  keycloak_1 | at org.keycloak.theme.DefaultThemeManager.getTheme(DefaultThemeManager.java:26)
  keycloak_1 | at org.keycloak.theme.DefaultThemeManager.getTheme(DefaultThemeManager.java:21)
  keycloak_1 | at org.keycloak.forms.login.freemarker.FreeMarkerLoginFormsProvider.getTheme(FreeMarkerLoginFormsProvider.java:262)
  keycloak_1 | at org.keycloak.forms.login.freemarker.FreeMarkerLoginFormsProvider.createResponse(FreeMarkerLoginFormsProvider.java:158)
  keycloak_1 | at org.keycloak.forms.login.freemarker.FreeMarkerLoginFormsProvider.createErrorPage(FreeMarkerLoginFormsProvider.java:498)
  keycloak_1 | at org.keycloak.services.ErrorPage.error(ErrorPage.java:31)
  keycloak_1 | at org.keycloak.authentication.AuthenticationProcessor.handleBrowserException(AuthenticationProcessor.java:728)
  keycloak_1 | at org.keycloak.protocol.AuthorizationEndpointBase.handleBrowserAuthenticationRequest(AuthorizationEndpointBase.java:145)
  keycloak_1 | at org.keycloak.protocol.oidc.endpoints.AuthorizationEndpoint.buildAuthorizationCodeAuthorizationResponse(AuthorizationEndpoint.java:409)
  keycloak_1 | at org.keycloak.protocol.oidc.endpoints.AuthorizationEndpoint.process(AuthorizationEndpoint.java:152)
  keycloak_1 | at org.keycloak.protocol.oidc.endpoints.AuthorizationEndpoint.buildGet(AuthorizationEndpoint.java:108)
  …
  </code></pre>