Cannot create a pipeline for blazor on VSTS - .net-core

Question

I've created a proof of concept blazor website on a VSTS repository. I wanted to setup a pipeline to build and test it but I've some issues.
In my visual studio, I've no troubles to build my solution, either by rebuilding the whole solution on Visual studio, either by running dotnet build my-sln.sln.
On VSTS, when I come to my build step, I've this issue:
2018-10-10T13:32:19.9132557Z ##[section]Starting: Build
2018-10-10T13:32:19.9137589Z ==============================================================================
2018-10-10T13:32:19.9137671Z Task : .NET Core
2018-10-10T13:32:19.9137712Z Description : Build, test, package, or publish a dotnet application, or run a custom dotnet command. For package commands, supports NuGet.org and authenticated feeds like Package Management and MyGet.
2018-10-10T13:32:19.9137754Z Version : 2.141.0
2018-10-10T13:32:19.9137806Z Author : Microsoft Corporation
2018-10-10T13:32:19.9137844Z Help : [More Information](https://go.microsoft.com/fwlink/?linkid=832194)
2018-10-10T13:32:19.9137901Z ==============================================================================
2018-10-10T13:32:20.7843899Z [command]C:\Windows\system32\chcp.com 65001
2018-10-10T13:32:20.9185978Z Active code page: 65001
2018-10-10T13:32:20.9791878Z [command]"C:\Program Files\dotnet\dotnet.exe" build D:\a\1\s\T-Dash.sln --configuration release
2018-10-10T13:32:27.3327317Z
2018-10-10T13:32:27.3330859Z Welcome to .NET Core!
2018-10-10T13:32:27.3331044Z ---------------------
2018-10-10T13:32:27.3331238Z Learn more about .NET Core # https://aka.ms/dotnet-docs. Use dotnet --help to see available commands or go to https://aka.ms/dotnet-cli-docs.
2018-10-10T13:32:27.3331363Z Telemetry
2018-10-10T13:32:27.3331657Z --------------
2018-10-10T13:32:27.3331810Z The .NET Core tools collect usage data in order to improve your experience. The data is anonymous and does not include commandline arguments. The data is collected by Microsoft and shared with the community.
2018-10-10T13:32:27.3332525Z You can opt out of telemetry by setting a DOTNET_CLI_TELEMETRY_OPTOUT environment variable to 1 using your favorite shell.
2018-10-10T13:32:27.3332584Z You can read more about .NET Core tools telemetry # https://aka.ms/dotnet-cli-telemetry.
2018-10-10T13:32:27.3332627Z Configuring...
2018-10-10T13:32:27.3332685Z -------------------
2018-10-10T13:32:27.3332740Z A command is running to initially populate your local package cache, to improve restore speed and enable offline access. This command will take up to a minute to complete and will only happen once.
2018-10-10T13:32:32.3411921Z Decompressing 0%Decompressing 1%Decompressing 2%Decompressing 3%Decompressing 4%Decompressing 5%Decompressing 6%Decompressing 7%Decompressing 8%Decompressing 9%Decompressing 10%Decompressing 11%Decompressing 12%Decompressing 13%Decompressing 14%Decompressing 15%Decompressing 16%Decompressing 17%Decompressing 18%Decompressing 19%Decompressing 20%Decompressing 21%Decompressing 22%Decompressing 23%Decompressing 24%Decompressing 25%Decompressing 26%Decompressing 27%Decompressing 28%Decompressing 29%Decompressing 30%Decompressing 31%Decompressing 32%Decompressing 33%Decompressing 34%Decompressing 35%Decompressing 36%Decompressing 37%Decompressing 38%Decompressing 39%Decompressing 40%Decompressing 41%Decompressing 42%Decompressing 43%Decompressing 44%Decompressing 45%Decompressing 46%Decompressing 47%Decompressing 48%Decompressing 49%Decompressing 50%Decompressing 51%Decompressing 52%Decompressing 53%Decompressing 54%Decompressing 55%Decompressing 56%Decompressing 57%Decompressing 58%Decompressing 59%Decompressing 60%Decompressing 61%Decompressing 62%Decompressing 63%Decompressing 64%Decompressing 65%Decompressing 66%Decompressing 67%Decompressing 68%Decompressing 69%Decompressing 70%Decompressing 71%Decompressing 72%Decompressing 73%Decompressing 74%Decompressing 75%Decompressing 76%Decompressing 77%Decompressing 78%Decompressing 79%Decompressing 80%Decompressing 81%Decompressing 82%Decompressing 83%Decompressing 84%Decompressing 85%Decompressing 86%Decompressing 87%Decompressing 88%Decompressing 89%Decompressing 90%Decompressing 91%Decompressing 92%Decompressing 93%Decompressing 94%Decompressing 95%Decompressing 96%Decompressing 97%Decompressing 98%Decompressing 99%Decompressing 100% 4694 ms
2018-10-10T13:33:07.6280747Z Expanding 0%Expanding 1%Expanding 2%Expanding 3%Expanding 4%Expanding 5%Expanding 6%Expanding 7%Expanding 8%Expanding 9%Expanding 10%Expanding 11%Expanding 12%Expanding 13%Expanding 14%Expanding 15%Expanding 16%Expanding 17%Expanding 18%Expanding 19%Expanding 20%Expanding 21%Expanding 22%Expanding 23%Expanding 24%Expanding 25%Expanding 26%Expanding 27%Expanding 28%Expanding 29%Expanding 30%Expanding 31%Expanding 32%Expanding 33%Expanding 34%Expanding 35%Expanding 36%Expanding 37%Expanding 38%Expanding 39%Expanding 40%Expanding 41%Expanding 42%Expanding 43%Expanding 44%Expanding 45%Expanding 46%Expanding 47%Expanding 48%Expanding 49%Expanding 50%Expanding 51%Expanding 52%Expanding 53%Expanding 54%Expanding 55%Expanding 56%Expanding 57%Expanding 58%Expanding 59%Expanding 60%Expanding 61%Expanding 62%Expanding 63%Expanding 64%Expanding 65%Expanding 66%Expanding 67%Expanding 68%Expanding 69%Expanding 70%Expanding 71%Expanding 72%Expanding 73%Expanding 74%Expanding 75%Expanding 76%Expanding 77%Expanding 78%Expanding 79%Expanding 80%Expanding 81%Expanding 82%Expanding 83%Expanding 84%Expanding 85%Expanding 86%Expanding 87%Expanding 88%Expanding 89%Expanding 90%Expanding 91%Expanding 92%Expanding 93%Expanding 94%Expanding 95%Expanding 96%Expanding 97%Expanding 98%Expanding 99%Expanding 100% 34027 ms
2018-10-10T13:33:41.4866462Z Object reference not set to an instance of an object.
2018-10-10T13:33:41.6079659Z ##[error]Error: C:\Program Files\dotnet\dotnet.exe failed with return code: 1
2018-10-10T13:33:41.6090166Z ##[error]Dotnet command failed with non-zero exit code on the following projects : D:\a\1\s\T-Dash.sln
2018-10-10T13:33:41.6128848Z ##[section]Finishing: Build
I don't really see what could be wrong here? Any idea?